Ram-X is a trade name that Pelican aquired when it bought the Coleman boat business almost 10 years-ago. The raw material is polyethylene. Pelican boats are built in a vacuum-thermoform process, from two sheets of the polyethylene material. The sheets are heated, then slid between a "top" and "bottom" mold. The clam-shell type mold is "closed," and a vacuum "sucks" the material into the mold cavities. The mold presses the two sheets together along the perimeter, creating a seemless monolithic shell.
The description SpeySpaz used above is actually for RamXcel, used in the construction of some canoes, but not kayaks. It's a rigid, closed-cell "foam" encased with "Ram-X" on each side. Allows for the construction of a canoe with the entire structure in the hull, without the use of additional keelson bars, etc.
The Polyethylene material is damn tough. It may get dinged-up a bit, but I don't know how you'd break it.
Pelican's recreational boats are constructed of Ram-X, while their Elite boats are built with "Poly XR" which is a higher-density material, more rigid, with a nicer finish/gloss to the product.
Polyethylene is widely used in the kayak market. Pelican is different in the manufacturing process, utilizing vacuum thermoforming vs rotomolding. Roto is more expensive and more time-consuming, but it does result in a little (cosmetically) nicer product, in the opinion of some.