It's a definitely a mylar touchpad. It feels more rigid than most but I'm a TrackPoint guy so I'm using the nub and dedicated buttons most of the time.
I just got a set of the Gen 7 in to test as replacements as our "lightweight" standard laptop as opposed to the Dell Pro 13 Plus we have been getting for the last year (we've had build quality issues with every lightweight Dell we end up going with) and so far my test group has loved them both for improved typing and the option to use the nub and buttons rather than the touchpad.