Perhaps if they were a few millimeters thicker my wheels wouldn't make dents they may end up cracking the surface. The dents sort of lock the chair in one place and makes it hard to move without some effort.
This is the third time I bought this item over the years. It wasn't available in the local store to see so they ordered it online for me. When it arrived I immediately noticed that this version appears much Thinner than the other two I have owned. Rolling around on it takes effort. Like the last two versions I suspect it will crack and discolor over time but with all things plastic that is normal. Simply stated "I'm not impressed".