This is an example of a Jon Renau Mono Top wig (their line of double-monofilament top wigs). Other brands may vary slightly. This is to give you a general idea of what to expect with this kind of cap construction, as most will be very similar.
The top of this wig is 100% hand-tied, just like on a monofilament top wig. Covering that is a layer of a smooth silk-like material that is put in place to protect the top of the scalp.
This type of cap construction is great for folks with sensitive scalps, but the trade-off is that it also tends to trap heat.