When players land on Kepler in Population Zero, they will need to find ways to protect themselves from all the things (and there are a lot!) that can kill them. One of the first things everyone will need is something to cover their bodies with, and on Kepler, there are two distinct types of gear players will need: Costume and Armor.
Costumes are similar to clothing and are worn closest to the body. "It protects players from temperature changes or toxic gas" and can boost stamina and HP. Players start off with a basic and upgradable costume. Upgrades can come from "plants, shipwreck scraps, rootsticks and ropes" at the beginning, but will require more advanced techniques and ingredients later. "Costumes can also be made with liquid substances" that protect from toxicity, cold or heat".
Armor, on the other hand, "is a set of plates defending from physical (i.e. crushing, slashing or piercing) damage". Players will be able to construct Armor from the plates removed from slain creatures. The more difficult the creature, the better the crafting resource.
You can read further details on the Population Zero site.