Great product, comfortable thick and lightweight, and I can confirm it is waterproof (I guess they all are to be honest) as I found out on my first use as I have it strapped to the outside of my backpack.
Dimensions are not advertised, it is 56cm X 185cm which is the largest mat I've had, I'm over 6Ft tall and my head and feet are all insulated from the ground which is great. They are also easily cut down with scissors if your either really small, or one of though weight saving boffins who use special titanium sporks to eat your freeze dried lightweight foods (you know who you are!)
I only have 1 niggle, its very, very flexible, and I guess if I tried I could tear this with my bare hands, so if your looking for something very robust it might not fit the bill. Overall I can put up with that at this price and it doesn't knock it down from top marks.
Great product 5*, please ignore the bad reviews people have given the product due to A) poor delivery times and B) they received the wrong item, as neither of these are reasons to put down good products, and should be left for 'Delivery/Outlet reviews, cheers for reading, hope this helped.