If you’ve ever wanted a fully customized CAS room to elevate your Sim creation experience, this guide will show you how to build a 3D CAS room mod from scratch! Inspired by LittleDica’s Old-School CAS room and ThatOneGreenLeaf’s CAS background tutorial, this step-by-step guide walks you through the process of designing a 3D room mesh using Blender, Sims 4 Studio, and GIMP.

Creating a custom Create-a-Sim (CAS) room in The Sims 4 allows you to design a unique environment that enhances your character creation process. This guide will walk you through the entire process—from setting up your room in Blender to importing it into Sims 4 Studio and applying textures. If you are a visual learner, like me, you can check out my YouTube video for a walk-through of my process!

Tools You’ll Need

To create your custom CAS room, you’ll need four programs:

  1. Blender – For 3D modeling the room.
  2. Sims 4 Studio – For creating the game package file.
  3. GIMP – For editing texture images.
  4. The Sims 4 – For testing the modded package file.

Make sure these programs are installed and working correctly before you begin!

Step 1: Extracting the Default CAS Room

  1. Open Sims 4 Studio and create a new object
    To start, launch Sims 4 Studio, a powerful tool used for creating and editing custom content for The Sims 4. Once open, select the “Create 3D Mesh” option to begin a new object. This will allow you to build and customize your own Create-a-Sim (CAS) room. After selecting this, you’ll be presented with various templates to choose from. For a CAS room mod, it’s best to start with a base room object that can be customized with furniture, textures, and other elements to match your vision.
  2. In the search bar, type ‘casroom’ and check the Show Debug Items box
    Now, you’ll need to search for an existing CAS room object as a starting point. In the search bar within Sims 4 Studio, type ‘casroom’ to filter items related to the CAS room. This helps you find the room’s base object quickly. After typing the search term, be sure to check the box labeled “Show Debug Items”. Debug items are hidden or experimental assets within the game, which can sometimes provide more flexibility or additional options for customization.
  3. Click Next, and name your package file (e.g., Joycasroom)
    After selecting the CAS room object, click Next to proceed. Here, you will be prompted to name your package file. The name you choose will be important because it determines how the mod is recognized in the game. A name like “_CasRoom” is clear and easy to remember. Choose something that represents the mod’s purpose and that will help you identify it later in your mods folder. Make sure the name follows a consistent naming convention to stay organized in your modding folder.
  4. Save your package file in your Mods folder
    The next step is saving the file. After naming your package, save the file in the Mods folder to ensure it’s properly integrated into The Sims 4 game. The default location for this folder is:
    Documents > Electronic Arts > The Sims 4 > Mods.
    This folder is where all your custom content (CC) and mods are stored. By saving your file here, you ensure that the game can recognize and load it when you start up Sims 4.
  5. Open the package file to view the default CAS room
    Now that your package file is saved, open it in Sims 4 Studio to review the default CAS room. This step allows you to see the room layout, textures, and meshes that come with the object by default. You’ll be able to observe the structure and components of the CAS room, such as walls, floors, and furniture, which you can modify to fit your desired design.

    Step 2: Understanding Textures & Meshes in Sims 4 Studio

    In Sims 4 Studio, navigate to the Texture Tab. You’ll see:

    • Two diffuse textures – These control the room’s appearance.
      Diffuse textures define the color and overall look of the object, such as the fabric on a chair or the wallpaper in a room. In Sims 4 Studio, you’ll typically see two diffuse textures for most objects. These textures are essential for determining how the object appears in the game world. For instance, if you are working on a couch, the diffuse texture will control the color of the fabric and any patterns that are displayed on it.
      • The first, a Diffuse texture with an Instance ID of 851A20DE22F57864, is responsible for the overall aesthetic of the room and will be modified to shape its visual appearance. This texture serves as the foundation for the room’s surface details, such as walls and floors.
      • Additionally, a second Diffuse texture with an Instance ID of DD3002938A8FCA18 will be dedicated to the mirror mesh, and it will be modified to define the look of the mirror within the CAS room.
    • One normal texture – This controls surface details (we won’t edit this).
      This texture is responsible for adding surface detail to objects, such as the appearance of wrinkles on fabric, the roughness of a stone surface, or the bumps on a textured wall. The normal map doesn’t change the object’s actual shape but instead makes it appear as though there are small details on the surface that create the illusion of depth. For this walk through, you won’t need to edit this texture, but it’s helpful to understand that it adds realism to objects by simulating surface imperfections. In many cases, you can leave the normal texture as it is, but it’s still important to know its function.

    Next, head to the Mesh Tab to check out the object’s structure:

    • This CAS room object has one mesh, with:
      • LOD 0 (High Detail)
        LOD stands for “Level of Detail,” and LOD 0 refers to the highest level of detail in the mesh. This is the version of the object that appears when you’re close to it in the game. The higher the level of detail, the more polygons the mesh has, making it look sharper and more defined. It’s important to understand that LOD 0 is what you’ll primarily be working with when you import and export the CAS room, as it defines how the objects will look up close. For this walk through, you don’t need to adjust LOD 0 unless you’re making detailed custom meshes.
      • Shadow 0 Mesh (Shadows for the model)
        This mesh represents the shadows cast by the object in the game. It’s essentially a special version of the mesh that defines how the object will project shadows onto the floor or surrounding surfaces. The shadow mesh does not impact the object’s appearance directly but is crucial for ensuring that the shadows look realistic in the game. It’s not necessary to adjust the shadow mesh, but understanding that it exists can help you when you start working with more advanced custom content.

    🔍 Bonus Tip: In the Warehouse Tab, you’ll find the Instance ID for each texture. This is useful for identifying which textures are linked to the model. In this tab, you’ll find all the Instance IDs for textures and meshes associated with the object. This is extremely helpful when you need to locate or edit specific textures. By referencing the Instance ID in the Warehouse Tab, you can easily see which texture belongs to which part of the object and ensure that you’re making the right adjustments.

    Step 3: Editing the Shader for a Flat Mirror in Sims 4 Studio

    In this step, you will adjust the shader settings to convert the object into a working mirror. Here’s a detailed guide on how to do that:

    1. Access the Warehouse Tab: Open your project in Sims 4 Studio and navigate to the “Warehouse” tab. In this section, you’ll find various components that make up the object. Scroll down the list of options until you locate “LODs” (Level of Details). This is where you can make adjustments to the object’s geometry and textures, including its shader settings.
    2. Modify the LODs: To begin making changes to the object, click on the “Edit Items” button. This will allow you to access and modify the underlying properties of the selected object.
    3. Edit Meshes: Under the LODs section, you’ll see an option labeled “Meshes.” Click the “Edit Items” button next to it to further adjust the object’s mesh, which is the 3D model. This step is crucial for ensuring that the mirror will function properly within the game.
    4. Adjust the Shader: Scroll down through the available options until you find the “Shader” setting. This is the part of the object’s material properties that defines how light interacts with its surface. Initially, the shader may be set to “Phong Alpha” by default, which is used for most objects. Change this setting from “Phong Alpha” to “Flat Mirror.” This will apply a reflective material to the object, allowing it to behave like a mirror in the game.
    5. Review New Values: After changing the shader to “Flat Mirror,” you will notice two new parameters appear in the list:
      • Mirror Plane Normal: This value determines the orientation of the reflective surface. It essentially defines the direction in which the mirror reflects.
      • Mirror Plane Offset: This value adjusts the position of the reflective surface, allowing you to fine-tune how the reflection is displayed relative to the mirror object. These two settings will need to be adjusted later in Blender to get the correct reflection behavior. However, before making those adjustments, it is important to first view the current reflection in the game. This will give you a better understanding of how to properly fine-tune the Mirror Plane Normal and Mirror Plane Offset values.
      • Save Your Package File: After making these changes, don’t forget to save your project. This ensures that all modifications are retained and the changes will be applied when you load the file again.

    ❗ Important Note: Keep in mind that Sims 4 Studio does not update the shader immediately. Although you’ve changed it to “Flat Mirror,” the object will still appear with the “Phong Alpha” shader until you save, close, and reopen the file. Don’t worry about this for now; it’s just a temporary visual discrepancy.

    Step 4: Exporting & Modifying the 3D Mesh in Blender

    Now that our CAS room object is set up, it’s time to export it so we can begin making edits in Blender. Follow these steps carefully to ensure everything is saved correctly:

    1. Return to the Studio Tab – In Sims 4 Studio, navigate back to the Studio tab, where you can access the details of the CAS room object you selected earlier. This is where you’ll find the option to export the mesh file for further editing.
    2. Click “Export Mesh” – Locate the “Export Mesh” button, typically found in the lower-right section of the interface. Clicking this will generate a Blender (.blend) file, which contains the 3D model of your CAS room. This file will be used for modifications, such as adjusting the shape, adding new elements, or optimizing the object for the game.
    3. Save with a Recognizable Name – When prompted, choose a clear and descriptive file name so you can easily identify it later. For example, instead of a generic name, use something relevant, like "CASRoom.blend". This ensures that you won’t confuse it with other exported files, especially if you’re working on multiple projects.

    Step 5: Adding a Mirror to the CAS Room

    To add a fully functional mirror to your CAS room, we need to extract a mirror object from Sims 4 Studio. This process will give us both the 3D mesh and the necessary textures to make the mirror look and work properly in-game. Follow these steps carefully to ensure you have everything you need:

    Extracting the Mirror Object

    1. Navigate to “Standalone Recolor” in Sims 4 Studio
      • Open Sims 4 Studio and go to the “Standalone Recolor” option from the main menu. This allows us to extract an object from the game files without modifying the original item.
    2. Select “Object” and Search for a Mirror
      • Click on the “Object” category to access all the available in-game objects.
      • In the search bar, type “Mirror” to filter the results and find a mirror that fits your CAS room aesthetic. You can choose any mirror, but a simple, minimalistic one works best.
    3. Choose Your Mirror and Save the Package File
      • Once you’ve selected a mirror, click “Next” to proceed.
      • You’ll be prompted to save a package file. Choose a name that makes sense for your project—I used “test.package” for this tutorial, but you can name it something more descriptive like "CASRoomMirror.package".
    4. Export the Mirror’s 3D Mesh from the Meshes Tab
      • After saving, go to the “Meshes” tab, where you’ll see different Level of Detail (LOD) options.
      • Select LOD 1 (Medium) – this is the optimal level for editing because it provides a good balance between detail and performance.
      • Click “Export Mesh” to save the 3D model as a Blender (.blend) file.
      • Name it “mirror.blend” so you can easily find and reference it later when integrating it into your CAS room.

    Extracting the Mirror’s Textures

    Once you have the mirror’s 3D model, you also need its textures to ensure it looks correct in-game. The mirror has two key textures: one for the glass and one for the frame.

    1. Open the Texture Tab in Sims 4 Studio
      • Navigate to the “Texture” tab within Sims 4 Studio, where the mirror’s textures are stored. These textures define how the object appears in-game, including colors and transparency.
    2. Export the Two Diffuse Textures
      • Look for the Diffuse Texture section—this contains the base textures for the mirror.
      • You will need to export two specific textures:
        • Mirror Glass Texture – This controls the transparent reflective part of the mirror. Click “Export” and save it as “mirror_glass.png”. This will later be used to set up the reflective shader in Blender.
        • Mirror Frame Texture – This defines the appearance of the mirror’s border. Click “Export” and save it as “mirror_frame.png”. You will apply this to the frame mesh to maintain its original look.

    Step 6: Editing the Mirror Texture in GIMP

    Now, let’s adjust the mirror texture to improve its visibility while working in Blender. By default, the mirror glass texture is nearly transparent, making it hard to see in the 3D viewport. To make editing easier, we’ll add a temporary overlay that won’t affect the final in-game result. Follow these steps carefully:

    Enhancing Mirror Visibility in Blender

    1. Open the Mirror Texture in GIMP
      • Launch GIMP (GNU Image Manipulation Program) or another image editing software that supports layers and transparency.
      • Open the previously exported “mirror_glass.png” file. This file is mostly transparent since it represents the reflective surface of the mirror.
    2. Add a New Layer with a Bright Color
      • In the Layers Panel, create a new layer above the existing mirror texture.
      • Select a bright, easily distinguishable color—I used pink, but you can choose neon green, blue, or any high-contrast color. The goal is to make the mirror glass stand out in Blender’s viewport while editing.
      • Fill the new layer with the chosen color using the Paint Bucket Tool (Shortcut: Shift + B).
    3. Export the File as a PNG (Preserving Transparency)
      • Before saving, ensure that your bright-colored overlay layer is semi-transparent by adjusting its opacity (around 50%) in the Layers Panel. This helps maintain some visibility of the original glass texture.
      • Go to File > Export As…, select PNG as the file format, and name it “mirror_glass_edit.png”.
      • Make sure the “Save transparency” option is checked to retain the original transparency properties.

    ⚠️ Important Note:

    • This pink overlay is only for editing purposes in Blender. It won’t appear in the final game.
    • Sims 4 Studio will still interpret this texture as a Flat Mirror Shader, meaning it will reflect properly in-game.
    • Once you’re done modeling and positioning the mirror in Blender, you can switch back to the original “mirror_glass.png” file before importing it back into Sims 4 Studio.

    With this visibility tweak, you’ll find it much easier to align and edit the mirror in Blender without struggling to see the transparent parts!

    Step 7: How to Perfectly Position a Mirror in Your Sims 4 CAS Room Mod

    Adding a functional mirror to your custom Sims 4 CAS room can take your mod to the next level. But simply placing a mirror isn’t enough—it needs to be properly positioned and fine-tuned to reflect your Sim correctly. In this guide, I’ll walk you through how to:

    1. Open & Prepare Your CAS Room Blender File
      • Locate your CAS room Blender file and open it.
      • Inside Blender, you’ll see two key meshes:
        • Studio Mesh 0 – The background image/mesh.
        • Studio Mesh 1 – The flat mirror mesh (this is the one we’ll be working with).
    2. Assign the Mirror Texture in Blender
      • In the Material Properties panel (bottom right in Blender), remove the circle image texture.
      • Click “Open” and select your mirror glass file to assign it as the new texture.
    3. Positioning the Mirror in Blender
      Now that the texture is assigned, we need to get the mirror into the correct position. Follow these steps:
      1. Rotate the Mirror Vertically
        • Select Mesh 1 (mirror).
        • Type “RX 90” and press Enter (this rotates it 90° on the X-axis).
      2. Move the Mirror Up
        • Press “G”, then “Z”, and move the mirror up until its bottom edge lines up with the floor.
      3. Scale the Mirror
      4. Press “S”, then:
        • “X” to scale horizontally.
        • “Z” to scale vertically.
      5. Set the Exact Dimensions
        • Press “N” to open the Item Panel.
        • Under Dimensions, set:
          • X = 1
          • Y = 2
          • Z = 0
        • Reposition the mirror to align properly with the scene.
    4. Adjust Mirror Rotation for a Natural Reflection
      1. Switch to Front View
        • Press “1” on the numpad.
        • Press “G”, then “Z” to adjust the mirror’s height if needed.
      2. Switch to Top View
        • Press “7” on the numpad.
      3. Rotate the Mirror for the Best Angle
        • Press “R”, then “Z” to rotate along the Z-axis.
        • Rotate it to around 25° for a natural reflection.
        • Manually adjust rotation values in the Item Panel:
          • X Rotation = 89°
          • Z Rotation = 19°

    💡 Tip: Keep playing with these values until the mirror appears the way you want in Create-a-Sim (CAS) mode.

    1. Import the Updated Mesh Back into Sims 4 Studio
      • Save your Blender file.
      • Open your CAS package file in Sims 4 Studio.
      • Under the Meshes Tab, click “Import” and select your updated Blender file.
      • The mesh may look odd at first—that’s because we still need to update the texture.
    2. Import the Mirror Texture in Sims 4 Studio
      • Go to the Texture Tab.
      • Select the second diffuse texture (the current mirror image).
      • Replace the circle image by importing your mirror glass texture.
      • Click “Save”.
    3. Test the Mirror Reflection in CASand Adjusting the Reflection Settings
      Now, let’s check how the mirror looks in Create-a-Sim mode! At first glance, you might notice:
      • The reflection doesn’t show much of the Sim—it mostly reflects the background.
      • The mirror’s reflective surface may not be facing the right way.

    To get the Sim centered in the mirror’s reflection, we need to tweak the X, Y, and Z values in Sims 4 Studio:

    • X Value (Horizontal Tilt):
      • Increasing X → Moves the reflection to the right.
      • Decreasing X → Moves the reflection to the left.
    • Y Value (Vertical Tilt):
      • Increasing Y → Tilts the reflection upward.
      • Decreasing Y → Tilts the reflection downward.
    • Z Value (Reflection Depth & Perspective):
      • Lower Z → Angles the mirror toward the ground.
      • Higher Z (above 1) → Can distort reflections.

    Be careful when adjusting Z! Extreme values can make reflections appear unnatural.

    1. Fine-Tuning the Mirror’s Normal Plane Offset
      By default, the mirror’s normal plane offset is 0, which makes the Sim’s reflection appear directly behind them—almost like they’re pressed against the mirror
      Fixing the Reflection Depth:
      1. Increasing the normal plane offset to 0.5.
      2. Now, the reflection will appear to have some distance between the Sim and the mirror.
      3. Keep adjusting this value until the reflection looks natural.

    💡 Tip: This is another area where trial and error is key—adjust the values until you get the perfect effect.

    Step 8: Building and Adjusting Your Sims 4 CAS Room in Blender

    Creating a custom Sims 4 CAS room requires precise mesh editing and positioning.

    1. Add a Cube Mesh
      • Open Blender and select Mesh 0.
      • Press Shift + A → Select Mesh → Click Cube.
      • Open the Item Panel (press N if it doesn’t appear).
      • Under Dimensions, set:
        • X = 4.5
        • Y = 5
        • Z = 2.5.
    2. Position the Cube Correctly
      • Adjust the cube’s Z location by changing the Z value from 0 to 1.25 (half of the cube’s height).
      • Switch to Top View by pressing 7 on the numpad.
      • Rotate the cube by pressing R, then Z to rotate along the Z-axis, then adjust the cube’s position using your mouse.
      • Finalize the cube’s location, set:
        • X = 0.43
        • Y = 0.78
        • Z = 1.25
    3. Removing Walls and Ceiling for Better Visibility
      • Switch to Edit Mode (Tab key).
      • Select the wall closest to us. Press P → Select Selection (this separates the panel from the cube).
        • Repeat this step for the ceiling by selecting the top of the cube and pressing P to separate it.
      • You should now see the wall and ceiling as separate objects in the Scene Collection.
    4. Refining the Room Using Loop Cuts:
      1. Cutting the Wall Panel:
        • Select the first separated panel.
        • Press Control + R to add a loop cut.
        • Adjust the yellow line slightly to the right, then left-click to lock it.
        • Switch to Face Select Mode (Press 3 on the keyboard). Delete the larger portion of the wall.
      2. Cutting the Ceiling Panel
        • Select the top panel.
        • Press Control + R and create two loop cuts:
          • The first cut should be dragged one-third to the left, and the second cut slightly thicker than one-third to the right.
          • Adjust cuts if necessary by selecting an edge and pressing G to move it.
          • Add another loop cut in the opposite direction by pressing Control + R, adjusting the position, and left-clicking to lock.
      3. Removing Unnecessary Faces
        • In Face Select Mode, select and delete the middle panel, top, right, and bottom-left panels.
    5. Merging the Room Structure
      1. Save a copy of your Blender file in case you need to revert changes.
        • Select Cube, Cube 001, and Cube 002, then press Control + J to join them together.
        • Remove the old Mesh 0 background by selecting Mesh 0 in Face Select Mode, pressing A, and then pressing X to delete faces.
        • Merge the new room structure with Mesh 0 by selecting Mesh 0, holding Shift, and selecting the Cube, then pressing Control + J (this should transfer the material from Mesh 0 to the Cube).
        • Ensure the cut values are correct:
          • Mesh Z cut = 0
          • Mesh 1 cut = 1
    6. Testing the Room in Sims 4 Studio
      • Save the Blender file.
      • Open Sims 4 Studio and load your CAS Room package file.
      • Under the Studio Tab, select Meshes → Click Import Mesh, then choose your Blender file and click Open.
      • Rotate the room in Sims 4 Studio to check for missing walls.
    7. Fixing Disappearing Walls with the Solidify Modifier
      • If walls disappear when rotating the room in Sims 4 Studio, open Blender and select Mesh 0.
      • Go to Modifier Properties (wrench icon). Click Add Modifier → Select Solidify Modifier.
      • Adjust the thickness by setting Thickness = 0.010.
      • Apply the modifier and save the Blender file.
      • Re-import the Blender file into Sims 4 Studio.
      • Rotate the room again to ensure the walls stay visible.
    8. Expanding the Ceiling to Cover the Sky in the Reflection of the Mirror
      • Open Blender and select the ceiling panel.
      • Switch to Top View by pressing 7 on the numpad.
      • Press S, then Control + Z to scale along the X and Y axes.
      • Increase the size slightly to cover the exposed sky that appeared in the mirror’s reflection.
        • Use G to fine-tune the panel’s position.
        • Save the Blender file and test in the game.

    Step 9: Importing Objects into Blender for The Sims 4: A Step-by-Step Guide

    If you’re diving into custom content creation for The Sims 4, you’ll need to understand how to import objects, manage textures, and align everything properly. This guide walks you through the process, from importing objects to finalizing them for use in the game.

    1. Importing Objects and Setting Up the Package File
      • Start by importing your objects into Blender.
      • Save all objects as a package file named “Test” (since we only need the mesh and texture, the package file itself won’t be necessary).
      • Click “Object” and use the search bar to find what you need (e.g., type “curtain”).
      • Select the test package file and overwrite it.
      • In the Texture tab, select your desired swatch color.
      • In the Meshes tab, click “Export Mesh” and save the Blender file with the object’s name (e.g., Curtain).
      • In the Texture tab, ensure that the Diffuse texture is selected and export the image file with the same name as the Blender file.
        • Repeat this process for all objects you want to import.
    2. Importing Wall and Floor Textures
      • Click the Build button and set the type to Wall.
      • If working with floors, change the type to Floor.
      • Select a game pack (e.g., Life and Death game pack) for textures.
      • Export the texture image and save it as “Wallpaper 1.”
      • Create a 4096×2048 transparent PNG file in GIMP to compile textures.
      • Scale each texture layer down to 25% of its original size and arrange them appropriately.
      • Wall and floor textures need to repeat for proper tiling in-game.
    3. Applying Textures in Blender
      • In Blender, enter Edit Mode and select object faces in the UV Editor.
      • Enable UV Sync Selection (icon with two arrows pointing opposite directions).
      • Apply a Subdivision modifier:
        • Go to Modifier Properties → Add Modifier → Subdivision Surface.
        • Select Simple to maintain shape.
        • Set Levels Viewport to 1.
        • Switch to Object Mode, apply the modifier.
      • Assign the texture:
        • Go to Material Properties.
        • Open the Shader Editor (change bottom window from Timeline to Shader Editor).
        • Unlink the existing texture, then open and import the new PNG texture file.
        • Enter Edit Mode, select faces, and align them to the texture in the UV Editor.
      • Adjust texture alignment:
      • Select the wall face in 3D viewport and match it in UV Editor.
      • Use S + X to scale along the X-axis.
      • Press G to move faces over the texture image.
      • Rotate faces as needed (press R, then adjust rotation in the bottom left menu to 90°).
      • Ensure the UV map is named “UV0” (required for proper game rendering).
    4. Importing and Aligning Objects
      • Append objects into Blender:
        • Go to File → Append.
        • Select the Blender file of the object.
        • Open the Object folder and select all Studio Mesh files.
        • Delete unnecessary rigs, bones, or extra Studio Mesh files.
      • Assign object textures:
        • Change the object’s texture to match the room’s texture in the Shader Editor.
        • Enter Edit Mode, select all faces (A), and align them in the UV Editor.
      • Position objects:
        • Press G + Shift + Z to move along the X and Y axes.
        • Use Top View (7 on numpad) for better alignment.
        • Position objects (e.g., align a sofa against a wall).
      • Join objects with the room:
        • Select the object’s mesh, then the room mesh.
        • Press Ctrl + J to join both objects.
        • Ensure the final object is named “Mesh Zero.”
        • Remove any unnecessary modifiers, vertex groups, and ensure the Cut value is set to 0.
    5. Adding Windows, Mirror Frames, and Backgrounds
      • Appending Windows:
        • Import the window mesh and delete unnecessary parts.
        • Duplicate the window if needed.
        • Position it against the wall.
      • Cutting Out Windows in the Wall:
        • Enter Edit Mode and use the Knife Tool (K) to outline the window. Select the cut-out face, press X → Delete Faces.
        • If the wall has doubled faces, remove both front and back faces.
      • Appending Mirror Frames:
        • Import and align the mirror’s faces to the room texture.
      • Adding a Backdrop:
        • Create a plane mesh (Shift + A → Plane). Rotate it 90° along the X-axis.
        • Assign it the room texture and align faces in the UV Editor.
        • Apply a Solidify modifier to ensure proper in-game rendering.
    6. Final Steps
      • Remove any leftover modifiers or vertex groups.
        • Verify that the UV Map is set to “UV0.”
        • Save your Blender file.
        • Open S4 Studio to finalize your work and test it in The Sims 4.

    Step 10: How to Fix Transparency Issues and Add Shadows in S4 Studio

    If you’re running into transparency issues in your Sims 4 CAS room, don’t worry—I’ve got you covered! In this guide, we’ll walk through how to fix black transparency issues and add realistic shadows using Blender and S4 Studio. Let’s dive in!

    Fixing Transparency Issues

    1. Import the Blender file and texture
      • Select “Import Blender Mesh” under the Meshes tab.
      • Navigate to the Texture tab and import the texture file.
      • If any items that should have transparency (like plants) appear black, we’ll need to fix them in S4 Studio.
    2. Editing the Mesh in S4 Studio
      • Open S4 Studio and go to the Warehouse tab.
      • Select Model > Data > LOD, then click Edit Items. Under Meshes, select Edit Items.
      • Since our issue is in the room’s mesh (not the mirror), scroll down and select Full Bright.
      • Click Edit Items under Material.
    3. Adjusting Alpha Settings
      • Find Alpha Blend Enabled and change it to Alpha Blended.
      • Change the Alpha Mesh Threshold from 0 to 1 (100) for full transparency.
      • Set Alpha Blended Value to 1.
      • Press Save and go back into Edit Items under Material.
    4. Creating an Alpha Map
      • Select the Diffuse Map and press Copy.
      • Change the new map’s field from Diffuse to Alpha Map.
      • The Alpha Map should be linked to the room’s texture, ensuring it displays correctly.
      • Save all changes and close the package file.
      • Reopen the package file to check: If done correctly, the black parts should now appear blue or transparent.
      • Test in-game—if transparency looks good, then you’re all set!

    Adding Shadows to the Room Mesh Texture File

    1. Setting Up Shadows in Blender
      • With the room mesh selected, go to Render Settings (the camera icon).
      • Change the render engine from Eevee to Cycles.
      • Expand the Bake section.
      • Change Bake Type to Ambient Occlusion.
      • Uncheck Clear Image.
      • Change the Margin Size from 16 to 2.
      • Press Bake and wait for it to complete.
    2. Editing Shadows in an Image Editor (I used GIMP)
      • Save the new shadow image from the UV Editor.
        • Click Image (top-left menu) > Select Save As > Choose a PNG format
        • Open an image editor (GIMP) and bring in the original texture and the new shadow image (place it on its own layer).
        • Lower the shadow layer opacity to 44.5%.
        • Remove unwanted shadows using box selection (e.g., from windows and transparent areas).
        • Change the shadow layer mode from Normal to Multiply.
        • Adjust opacity as needed (I kept mine at 26.5%).
        • Export the new image as a PNG.
    3. Updating the Texture in Blender & S4 Studio
      • In Blender’s Shader Editor, replace the old texture with the new shadow texture.
      • Save changes and replace the texture in S4 Studio.
      • Open the CAS room to check the final result.

    That’s It, That’s All!

    Modifying the Sims 4 CAS room using Blender, GIMP, and Sims 4 Studio is a rewarding process that allows you to personalize your game in unique ways. Whether you’re adding a functional mirror, adjusting textures, or completely redesigning the space, mastering these tools opens up endless creative possibilities. By carefully exporting meshes, refining textures, and testing your modifications, you can create a polished, immersive CAS room that enhances your Sims’ customization experience.

    I hope you found this guide helpful and it encourages you to explore more of Blender and Sims 4 Studio. If you’re ready to see these techniques in action, check out my downloadable CAS room mod—fully customized and ready to use in your game! Download it now and start transforming your Sims’ world. Happy modding! If you found this useful, make sure to hit that like button—GG’s! 😉