In general, almost all of the manufacturers try to use materials that are water-resistant. That is one of the essential things to look for. However, most of the cheap ones may have lower-quality materials and they might rust and deteriorate over time.
The good quality ones can be made of plastic, like phenolic or high-density polyethylene that are lightweight materials and very resistant ones as well. They are also non-porous, which makes it easier to clean them.
Mold resistant woods are also a good choice because they are very strong materials. These include teak and bamboo. The seat should also have a stainless steel or aluminum frame so that it offers great stability and sturdiness.
These materials are not prone to rust, so they will ensure the durability of the product. They will also add robustness and steadiness for heavy people who need to use these types of chairs.