[dentstudent (OP)]

We have an anti-slip bathmat which is a sort of rubberised plastic. It's obviously been wet and remains wet for longish periods. As a result, a black mold has grown within the plastic itself, so it's not on the surface, but has turned patches of the mat black.

Can anyone tell me what it is, and how it survives?

[Karen W.]

I have seen this happen and could not figure it out! The only thing I could think was that the rubberized plastic is still a fiber right.. derived from a rubber plant wouldn't that tend to make the finished product more porous and able to retain bacteria and mold..Be more absorbent with longer exposure or soaking of the  surface?

[dentstudent (OP)]

It could be, but I think that many of these are also oil based and so have no natural fibres.

[Karen W.]

I did a google but there was so much information I could not sort out all the mixes..LOL