I have a rubber mat, also, but mine has little "grass blades" coming out of it for texture, these "blades" massage my feet while I shower. It has suction cups for the bottom. Each week I take it out and wash it in my washing machine with bleach and hot water, then hang over the bathtub to dry. I'm sure I got it at Walmart...
My doctor is very pleased because all those blades really give my feet a good cleaning and help with circulation (a serious problem of mine). I've had this mat a year and there seems no wear or anything. It is also antimicrobial, so I've never seen mold.