UV packing and padding

Packing is arranging UV islands inside the 0–1 square so they use as much of the texture as possible. Padding is the empty space you leave between islands, and the colour you bleed into it, so that neighbouring islands do not leak into each other.

Both are trade-offs: tighter packing means sharper textures, but too little padding causes visible seams once the texture is filtered and mipmapped.

#Packing efficiency

Every pixel outside an island is memory you pay for and never see. A bad layout can easily waste a quarter of the texture: KrisLW on Polycount says "I wouldn't be surprised if at least 1/4th - or more - of your map is empty" in a typical beginner layout (Polycount: Reducing UV Waste Need Help).

Opinions on acceptable waste vary. In a 2015 critique, ZacD called "under 25% wasted" fine, and WarrenM said 17% waste "is not bad by any means" (Polycount: Are these UVs good?). As a quick reference, the cross-shaped cube unwrap in UV mapping uses only 37.5% of the square, so almost two-thirds is wasted.

Ways to pack tighter, from the same threads:

• Straighten islands. Rectangular islands stack closely. Bek notes straightening round caps adds a couple of vertices and some distortion "but you're saving a lot of space" (Polycount: Reducing UV Waste Need Help).
• Group by shape. Put rectangles in corners, which Joost calls "the easiest to stack" (Polycount: Are these UVs good?), and group circles with circles (Polycount: Reducing UV Waste Need Help).
• Nest islands. Mark Dygert: "Don't forget that you can put UV shells inside of other ones" (Polycount: Reducing UV Waste Need Help).
• Stack identical parts. Repeated screws or bolts can share one island (Polycount: Reducing UV Waste Need Help). See the mirroring warning in UV mapping.

Automatic packers handle most of this. Blender's Pack Islands can rotate islands "as well as translation and scaling, to optimize texture usage" (Blender Manual: Editing). RizomUV reworked its packing in 2022, partly because of growing UDIM use in games (80 Level: Meet RizomUV 2022).

#Padding

#Mipmaps and padding

A texture in a game is stored with mipmaps: smaller copies at half, quarter and eighth size, used as the surface gets further away (Polycount: Padding!). Each mip halves the pixel count in both directions, so a gap of 16 px at full resolution is 8 px at the next mip, 4 px at the one after, and so on.

When the gap shrinks below a pixel, one pixel covers both islands and their colours mix. Mark Dygert explains that larger, chunkier pixels at low mips let the empty area bleed into UV space and cause seams (Polycount: Padding!). JohnnyRaptor adds that padding exists so that mipmapped textures do not get colours "bleeding in at the borders" (Polycount: Edge padding for game characters).

#Values per resolution

A 2012 Polycount thread quotes these edge padding guidelines, apparently copied from the old Polycount wiki (Polycount: Can not get the right padding):

The same text adds that "It works best when the UV gutters are at least twice this width", and that the values "apply differently depending on the engine, filtering type, and mip map mode" (Polycount: Can not get the right padding). In 2017, EarthQuake suggested "16 pixels between islands at 4k is probably fine for many cases" and called 16 to 32 px "pretty safe for a 4k texture"; 32 px is only needed if you expect a 4K texture "to be mipped down to 128 and still hold up" (Polycount: Padding!).

#Padding for lightmaps

Lightmaps are tiny, so the same rule produces large percentages. Epic's old UE3 guide says "4 texels are usually required to avoid all bleeding, as DXT compression operates on 4x4 texel blocks", so "for a lightmap resolution of 32, the padding between the UV charts should be 12.5% of the entire UV space" (Unreal Development Kit documentation: Unwrapping UVs for Lightmaps). See lightmap UVs.

#Dilation

Dilation (also called edge padding or bleeding) fills the empty space around each island with that island's edge colour. Even if a low mip mixes neighbouring pixels, it mixes similar colours, so no seam shows.

Every baker does this. Substance's bakers "Dilate/extend the pixels of the UVs outside or their border by the amount of pixels given" (Substance 3D Bakers documentation: Common parameters). Blender's bake Margin extends the result "this many pixels beyond the border of each UV island" (Blender Manual: Render Baking). Marmoset's padding "determines how far to extend the baked content past the UV borders" and adjusts automatically to resolution (Marmoset: The Toolbag Baking Tutorial).

Note that dilation fills the gap but cannot create one. Bal argues "There can't be too much edge-padding", but stresses leaving enough space between shells during unwrapping (Polycount: Edge padding for game characters).

#Orientation and pixel alignment

Edges that run at an angle across the pixel grid are drawn as stair-steps. Substance's documentation: "Aliasing often occurs because the geometry of the UVs is not aligned with the pixel grid" (Substance 3D Bakers documentation: Aliasing on UV seams). Its fixes are a higher resolution, more anti-aliasing, aligning UVs "to the pixel grid", and a better texel ratio (Substance 3D Bakers documentation: Aliasing on UV seams).

So orient islands with straight edges horizontally or vertically, and align strips with the direction of the texture detail (wood grain, panel lines, text).

#Island scaling priority

Islands do not all need the same amount of space. A common order of priority:

1. What the player sees closest and most: the front of a prop, the top of a table, the grip of a first-person weapon.
2. Everything else visible, at the project texel density.
3. Rarely seen areas: darkchief117 suggests shrinking "anything that will almost always be obscured from the player view or made black by a lightmap" (Polycount: Reducing UV Waste Need Help).

Two cautions from the same discussions. DWalker notes small parts like "handles, pipes, and screws could probably use the normal texel density" rather than extra (Polycount: Reducing UV Waste Need Help). And Joost warns that scaling down low-priority islands too early is a mistake (Polycount: Are these UVs good?): pack first at equal density, then shrink only what is truly hidden.

#In different tools

• Blender: Pack Islands with a Margin and Margin Method, optional rotation (Blender Manual: Editing); Average Islands Scale first to equalise density (Blender Manual: Editing).
• Maya: Unfold's Room space (pixels) "prevents textures from bleeding past the UV borders"; the docs advise against raising it above the default of 2 px because it slows the solve (Maya 2026 Help: Unfold UVs options).
• RizomUV: packing with custom scale and texel density settings (80 Level: Meet RizomUV 2022).

#Further reading and watching