It varies.

First aid and trauma pouches are well-marked cordura. Radios get similar with some light padding. Many other components are in gallon or quart freezer-rated Ziploc bags. Generally, if it’s a pouch I don’t expect to open often (none of the stuff in the Fire Now! module expires) or is very sensitive to water, it’s probably in a Ziploc.

A company called First Tactical (no affiliation) makes a variety of well-made, good looking and rugged pouches, many of mine come from them.