Protects you from
most of what the cave can throw at you ie water and sharp bits. It should be
hardwearing and waterproof or at least water resistant.
TSA make a bright yellow PVC oversuit that is both hardwearing and waterproof, unfortunately they're quite expensive (about £90) and you sweat buckets. Most manufacturers (Dragon, Warmbac, Dalesware etc) produce nylon/cordura versions for about £60-80.
Keeps you warm
and dries quickly. Constructed from man-made fibres, there are two types; Fleece
and Fibre-pile. Fleece is lighter and dries most quickly whilst Fibre-pile is
cheaper and warmer.
Depending on conditions it is usually wise to wear a layer close to the skin, such as a thermal of some type.