Different jobs require different materials, so manufacturers offer manways in various types of materials. This includes the standard stainless-steel options such as T304, T316L or 1.4301, 1.4404, etc. If you are in a corrosive industry, consider getting a manway with exotic duplex or Hastelloy construction.
Other materials include PTFE, FPM, EPDM, Buna-N, NBR, or Silicone Gaskets as sealing materials to eliminate crevices.
Material finishes are not standardized. Depending on your industry, you can get the manway cover in polished ID/OD from 2B to 400-grit finish.