What Minecraft Armor Trims Do
Armor trims are cosmetic decorations applied at a smithing table. A trim pattern decides the shape, while the material decides the color. The armor base still controls the actual armor item.
This viewer is built for fast comparison: pick the armor piece, choose the trim material, then choose the smithing template pattern. Each armor slot can be edited separately, so a helmet can use one material while the chestplate, leggings, and boots use another.
The 3D preview is only visual. It does not change armor strength, protection, durability, enchantments, or movement. A diamond chestplate with a redstone trim is still a diamond chestplate; the redstone only changes the trim color.