First and foremost, what exactly is mesh lining? Mesh is constructed of polyester and nylon, which are synthetic materials.
Mesh allows air to flow and enhance ventilation, allowing you to cool down and sweat more rapidly. The panels and lining are constructed of a knitted fabric that allows for a lot of mobility and elasticity.
Is it possible to wear mesh in the water? Yes, if they're made of polyester, nylon, or another synthetic substance. However, cotton boxers or underwear briefs are not recommended.