Franco,
G'day mate,
The Warmlite DAM is 3"/ 75 mm high when inflated.
Stephensons say not to inlfate fully, just to give enough air to support yourself prone. The instructions say to blow it up to the point where you can press your knee on the mat and contact the ground. I prefer it a bit less inflated than that, from my tests. It is easy enough to deflate a little while you are lying on it to get it right.

Here's a shot with a size 8 (US) North Face trail runner.
When I lie on it, the sides go up to 4"/ 100 mm. This is normal, according to the instructions from Stephensons, as it should act as a warming zone on the sides.

Here's a shot of it full length with the same shoe for scale. Gotta love that colour- no trouble finding this mat in the dark!!
The mat is very even, and the construction is first rate.
I hope this helps,
cheers,
fred