Trim sheets

A trim sheet is a texture divided into horizontal strips, each of which tiles left to right. Mouldings, panel edges, pipes, skirting boards, bevels and rows of bolts all live on one sheet, and many different meshes place their UVs on whichever strip they need. Tim Simpson calls trim textures "absolutely the backbone of most environment work" (Polycount: TUTORIAL: Trim Textures for environment art…).

Where a tileable material repeats in both directions and fills a surface, a trim repeats in one direction and runs along an edge or a band.

#Why studios use them

Memory. One sheet replaces dozens of unique textures. Tim Simpson says trims matter "especially when dealing with tight memory budgets", keeping "a crisp texel density without relying on massive 4k unique unwrap textures" (Polycount: TUTORIAL: Trim Textures for environment art…).

Fewer materials. Every mesh that uses the sheet shares one material, so the engine can batch them more easily (see draw calls). Tim Simpson also suggests non-square sheets such as 1k × 4k or 2k × 4k as "a good way to reduce drawcalls" when a mesh set shares one material (Polycount: Creating Trim Sheets 4 Part Tutorial…).

Consistency and speed. Once the sheet exists, texturing a new kit piece is a UV job, not a painting job. On DOOM Eternal, Chase Long describes a workflow that "leans heavily on tiling materials and trim sheets" and allows "fast creation and iteration but also plenty of sharing all around" (80 Level: Designing Environments for DOOM Eternal).

Portfolios. Tim Simpson writes that over half of junior environment applicants have "ZERO examples of tiling texture use or trim sheet knowledge in their portfolio", and that he would trust an applicant more with "a strong use of trim textures in at least one portfolio piece" (Polycount: TUTORIAL: Trim Textures for environment art…).

#Anatomy of a sheet

A typical sheet for one material family (stone, painted metal, wood) contains:

• Wide strips for big features: cornices, door frames, large panels.
• Thin strips for small trims, cables, seams and edges.
• Bevel strips: flat colour with a normal map that fakes a rounded edge (see the Ultimate Trim below).
• A flat or near-flat area that can act as a small tileable for filler faces.
• Unique-ish cells for a vent, a grate or a plaque, if the budget allows. These do not tile.

Tim Simpson's advice: keep each sheet to one material type, such as all metal or all stone, because mixed roughness values are harder to tune in the engine. Avoid copying the top half of the sheet with small changes, which wastes memory; make the trims more varied instead (Polycount: Creating Trim Sheets 4 Part Tutorial…).

Not every trim sheet is a stack of plain strips. EMC3D's video on trim types sorts them into two types plus a "modern hybrid", with examples from Assassin's Creed (a boat and a castle), 45-degree corners, asset skirting and a Bizarre Creations art test (YouTube: The Different Types Of Trim Sheets & How They…).

#Layout rules

1. Plan from the kit. Tim Simpson's first video in his series is entirely about planning which pieces a sheet must serve (Polygon Academy: Planning & Creating Trim Sheets For Games…). On Polycount he says "the less winging it the better usually" and recommends working backwards from designers' proxy models (Polycount: Creating Trim Sheets 4 Part Tutorial…). Nicolas Bucco's course likewise puts trim sheet planning straight after planning the modular kit (ArtStation Marketplace: Modular Building Kits and Trim Sheets Course).

2. Fix the texel density first. The sheet's pixel size and your texel density decide how big each strip is in the world. Beyond Extent says to "match your trimsheet layout as well as match the texel density of the scene", applying the target density to the UV islands first and then scaling them to the closest strip, usually within "around 25% up or down" (Beyond Extent: Texel Density).

3. Make strip heights powers of two, and start each strip on a multiple of its height. The rule follows from how mipmaps work. Each mip level halves the texture. A strip 256 px tall that starts at row 512 still starts and ends on whole pixels at 1/2, 1/4 and so on down to 1/256 size. A strip 300 px tall starting at row 400 does not: at 1/8 size it would run from row 50 to row 87.5, so the bottom pixel mixes two strips. The TrimForge add-on for Blender builds this check in: it warns about strips "narrower than 16 px" and non-power-of-two resolutions, and pads strips so they "are aligned to the mip levels" (Superhive Market: TrimForge — Trim Sheet Workflow).

4. Leave padding. Even aligned strips bleed into each other as mips blur. In the Ultimate Trim thread, Makkon stresses that "padding is very important", and Epitaph points out that lower-resolution versions of a trim need more padding to avoid bleeding (Polycount: The 'ultimate trim' technique from Sunset…). See UV packing and padding.

5. Tile horizontally, and test it. Every strip must wrap seamlessly at its left and right edges. Polynaught noticed seams where the two ends of a circular trim met; Tim Simpson replied that the seam is tiny and that "in 99% of cases you will never notice it" (Polycount: Creating Trim Sheets 4 Part Tutorial…).

#Making the sheet

Plan before you build. EMC3D's follow-up video on trim planning (September 2024) is organised as a process: a colour overlay plan, then a trim sheet plan, a warning not to rush, when to start trim sheets, using the blockout, and a recommended process (YouTube: What Does Good Trim Sheet Planning &…). The order matters: the blockout tells you which strips the kit actually needs, so the sheet is planned from the level rather than invented in isolation. See blockout and modular kits.

There are three common ways to build the content of a sheet. They can be mixed.

• Model or sculpt, then bake. Build the strips as real geometry (or sculpt in ZBrush) lined up on a plane and bake them down. Tim Simpson's series sculpts the strips in ZBrush and finishes them in Substance Painter (Polygon Academy: Trim Texture Tutorial - Environment Art 101). FastTrack's course builds trims partly in Maya and Painter and bakes in Marmoset Toolbag (ArtStation: Creating Advanced Trim Sheets for Games).
• Build it in Substance 3D Designer. Fully procedural, easy to change. See procedural materials.
• Paint it. For stylised projects, the strips can be hand-painted like any other texture. See hand-painted and stylised texturing.

#The Ultimate Trim (bevelled trims)

At GDC 2015, Morten Olsen of Insomniac Games presented "The Ultimate Trim", the technique a small team used to texture the open world of Sunset Overdrive. It used a specific trim layout and normal map structure to improve production speed, memory and performance, supported by a UV mapping script and a custom shader (GDC Vault: The Ultimate Trim: Texturing Techniques of…).

The core idea, as artists reconstructed it on Polycount: the sheet contains strips whose normal map encodes a bevel at an exact 45 degrees. A real mesh gets small chamfered edges, and those chamfer faces are UV-mapped onto the bevel strips, so the normal map makes the hard chamfer read as a smooth rounded edge (Polycount: The 'ultimate trim' technique from Sunset…).

What the Polycount thread found when people tried to reproduce it:

• The angle must be exact. dzibarik says "the secret to techinque was a PERFECT 45 degree angle on a normal map" and built his strips from planes rotated to 45 degrees (Polycount: The 'ultimate trim' technique from Sunset…).
• Vertex normals matter. huffer warns that bevels "will introduce shading gradients on planar surfaces, unless you use face-weighted normals" (Polycount: The 'ultimate trim' technique from Sunset…). See weighted (custom) normals.
• Seams versus hard edges. Makkon found that "hard-edges are much more noticeable than a texture seam on a flush surface" (Polycount: The 'ultimate trim' technique from Sunset…).
• Tools help. dzibarik judged it impractical without tools to manage UV islands; in 2024, AlexeyFanta noted that RizomUV had added trim sheet tools with padding controls (Polycount: The 'ultimate trim' technique from Sunset…).

Tim Simpson calls bevel size a style choice: for hard-surface sci-fi, a "chunky bevel" fits better than the smoother Sunset Overdrive look (Polycount: Creating Trim Sheets 4 Part Tutorial…).

#UV workflow

1. Model the piece to the grid of your kit (see grids and metrics).
2. Unwrap and straighten. Each band of faces that will use a strip becomes a straight, rectangular UV island.
3. Set texel density to your project target.
4. Snap islands to strips. Move each island vertically onto the right strip; let it run off the left or right edge freely, since the strip tiles.
5. Adjust the mesh, not just the UVs. Tim Simpson warns you will often "squash and stretch parts of your mesh" or add edge loops so pieces fit the trims (Polycount: Creating Trim Sheets 4 Part Tutorial…).
6. Check in the engine under real lighting, with a moving light on bevels.

Tim Simpson's fourth video covers UV mapping tips for this process (Polygon Academy: Trim Texture Tutorial - Environment Art 101).

#Examples

#Common mistakes

• Designing the sheet without a kit. Combining sheets after the fact can mean re-UVing "100s of modular pieces" (Polycount: Creating Trim Sheets 4 Part Tutorial…).
• Odd strip heights that blur together in lower mips.
• No padding between strips, so colours bleed at a distance.
• Using one hero strip everywhere. The repetition is easy to spot.
• Mixing materials on one sheet (metal next to stone), which makes roughness hard to tune (Polycount: Creating Trim Sheets 4 Part Tutorial…).
• Inconsistent density: strips scaled far more than ±25% look sharper or blurrier than their neighbours (Beyond Extent: Texel Density).

#Further reading and watching