Leather

It has exactly one destination, the archaeologist outfit, and that outfit is cosmetic. So this is a collector's material rather than something a progression run needs to stop for.

The catch is the input. It is built from rotten chunks, which only drop in a Corruption world; a Crimson world produces vertebrae instead and cannot make it at all. If you want the set on a Crimson save you have to grow a strip of artificial Corruption from Corrupt Seeds, or drop a Corrupt Statue and farm the eaters it spits out. Both work, and both take longer than the cosmetic reward justifies unless you are chasing completion.