Tanned, dried, scraped human skin. Most people find this material horrifying. Some find it fascinating. While a decent leather, it neither protects nor insulates particularly well.
The following animals provide human leather.
Human leather is an abundant and valuable resource, but comes with several downsides. The first is that buchering of humans to acquire the leather inflicts both a colony-wide mood debuff and a mood debuff to the cook that stacks per corpse butchered. Additionally, seeing human corpses yet another debuff. Pawns with the Bloodlust, Cannibal, or Psychopath traits are immune to all three debuffs however. These traits and other strategies can be used to minimize the impact of these penalties.
The second is that while human leather may be used as a crafting ingredient like any other leather, because of its horrifying origins, colonists without the Cannibal or Bloodlust traits will get a -2 mood debuff for each such item of human leather clothing worn, up to a maximum of -8. Colonists with the Cannibal or Bloodlust traits will instead get +2 for each item, up to a maximum of +8. Its use in other items such as furniture is unaffected.
Lastly, human leather is one of the least protective textiles in the game, at tied 21st most protective, or tied 8th least protective. It has terrible insulation, being the 4th and 3rd worst for heat and cold respectively.
Despite this, its abundance and oddly high market value mean make it a valuable tradegood, especially if processed into a high quality item of clothing or furniture first. Additionally it can be useful for a cheap, accessible and sustainable mood boost for Cannibal or Bloodlust pawns, however its terrible protective qualities mean that its use should be limited to skin layer clothing such as pants, while dusters should be made out of something more protective. Care must also be taken to prevent other pawns from wearing these items however, lest they get the mood debuff. Setting a custom outfit for the relevant pawns can help in this regard, such as banning tribalwear for all normal pawns and only making tribalwear out of human leather.