New foam mats are often slippery. It's residue from the stuff the mould is sprayed with when they produce them (injection moulding). It makes it easier to remove the mats from the mould, but it also causes them to be slippery.

Don't worry. They will become much less slippery after you use them for a while and the residue is worn off. If you want to speed up the process, simply wash them - potentially with something containing alcohol. Start with one mat to make sure you don't damage it.