UV unwrapping explained for people who just want good textures

A texture is a flat image. A model is a 3D surface. Before the image can be painted onto the surface, every face of the model needs a position on the flat image. That mapping is the UV map, and the process of creating it is UV unwrapping. The name comes from the axes of the texture image, U and V, used so they are not confused with the X, Y and Z of 3D space.

The classic analogy is a cardboard box: cut along some edges, fold it flat, and you can print on it. Unfold it, print, fold it back, and the print wraps the box. The cuts are seams and each flat piece is an island.

Seams: where the surface is cut

Any closed shape has to be cut to lie flat. A sphere cannot be flattened without either cuts or stretching, which is why world maps are always distorted somewhere. On a model, seams are where the texture may show a visible line, because neighbouring pixels on the surface are far apart on the image.

Good practice is to hide seams where they will not be seen:

• Along natural edges and creases, such as the corner of a crate or the inner leg of a character.
• On the underside or back of an object.
• Along material changes, where a colour change happens anyway.

Islands and how they are packed

Each island is a group of connected faces laid flat. Islands are then packed into the square texture like pieces in a box. Two things matter:

• No overlaps, unless intentional. If two islands share pixels, both parts of the model show the same paint. Sometimes that is a deliberate trick to save space, for example mirrored halves of a symmetric object, but it breaks unique details like scratches or text.
• Padding between islands. Texture filtering and lower mip levels blur neighbouring pixels together; without a gap, colour from one island bleeds into another at a distance.

Texel density: keeping detail even

A texel is a pixel of the texture as it appears on the model. Texel density is how many texels cover a given area of surface, for example pixels per metre. If one part of a model gets a large island and another a tiny one, the first looks sharp and the second looks blurry, even though they share one texture.

Consistent texel density matters most when several assets sit side by side in a scene; a crisp barrel next to a blurry crate looks wrong. Most engines and tools can display a checker texture to show density at a glance: squares should look the same size everywhere.

Why AI-generated models often need new UVs

Generated meshes and 3D scans usually come with automatic UVs made of many small, irregular islands. They work for the texture the model was generated with, but they are hard to repaint by hand and waste texture space. That is why threeD’s texturing tool checks UVs first and creates a fresh unwrap when it finds overlaps or poor density.

If you remesh a model, its old UVs no longer apply to the new surface. The original texture has to be baked onto the new UV layout, which threeD does as part of remeshing.

A quick UV checklist

1. Apply a checker texture. Are the squares roughly the same size and not stretched?
2. Are seams in places the camera will rarely see?
3. Are there overlapping islands you did not intend?
4. Is there padding of a few pixels between islands?
5. Does the layout use most of the square, without large empty areas?

For what goes into the texture once the UVs are right, see PBR texture maps explained.