Thanks for the useful advice. But I think you are talking about the carpet type mats?
I have an issue with the rather strange ‘all weather’ mats that BMW sell as an accessory. They are not rubber but seem to be made of an obscure material with a coating on. Light grey colour - which was a pretty dumb idea in the first place. I have tried a number of cleaners but so far without any success.
That is the one. No idea what they are made of. They are on a rubber base and the grey inserts also feel like rubber but with a clear coating. They are solid like a rubber mat - not a carpet like material.
There has got to be something that cleans them but I have not found it yet!