HD Minecraft Skins (128×128)

An HD skin is 128×128 pixels instead of the standard 64×64, which is four times the pixel count in the same layout. That extra room goes into things a standard skin cannot hold: fabric texture, individual strands of hair, embroidery, fine armour detail and readable patterns on small faces like the sides of the head.

The catch is support. Vanilla Minecraft Java accepts HD skins through the launcher, but a number of servers, older launchers and Bedrock skin packs still expect 64×64 and will either reject the file or render it wrong. If a skin below will not upload somewhere, that is usually why, and a 64×64 skin is the fix.