I'm looking for a chair mat to protect the carpet in an apartment from the wheels of an office chair. The suitability of all of the chairmats is described in terms of things like the pile of the carpet (e.g. low, medium, high) and whether or not it has padding. For example, this is the description from one of the mats I looked at: "for commercial and low pile carpets without padding".

I don't really know what all of that means. I don't know if the carpet has padding or how high its pile is. I'm looking for a mat to protect the carpet, so I don't want to damage it by using the wrong kind of mat. All I know about the carpet is that it's wall to wall and it's in an apartment. I'd describe it as relatively low / flat.

Can anyone help me with some advice on determining the characteristics of the carpet -- what kind of pile it has and whether it has padding -- or other advice on how to choose the right kind of mat?