Specifically, I mentioned...
But, I don't have them in a basement, so if it's particularly damp I suppose it _could_ be a problem. But, in the shop I only place them in the places where I normally stand frequently, like in front of the tablesaw, bench, etc., etc. Consequently, they're easy enough to flip over and move if want one somewhere else temporarily. The particular ones I was thinking of aren't solid, either, so that the amount of moisture entrapped wouldn't be that much (again, unless it were _really_ damp). They have about a 50% or more open spacing. Does mean they collect the sawdust in the holes, but as they're not that heavy, as noted above, all it takes is flipping one over to sweep. Most of the time the shop vac w/ the floor sweep tool is enough, anyway, though.
HTH...
OBTW, they were even cheaper than the solid ones by almost the 50% factor so I gather they're basically priced on the amount of material since they're mostly an artificial rubber, they're pretty much tied to petro prices. I also have a thin, salvaged truck bed liner that I didn't want in the truck that came w/ the used truck I bought that I've tossed on the floor in front of the chopsaw bench -- it isn't nearly as comfortable as the others, but even it helps noticeably both for softer standing and not so cold in winter.