Thickness, at the most is between 1/16 and 1/32 of an inch. It's really like a very THICK high quality poster. I didn't put lexan over mine simply because I was satisfied with the quality of the coating and felt it wasn't necessary.
The lip around the edge made by the t-molding is noticeable, but certainly not a neusance and not something that's going to come loose or cause a problem.