You may be thinking of Old Town "3-layer superlinear" plastic. It has a layer of foam sandwiched between two layers of plastic.
Read about it at http://www.oldtowncanoe.com/craftsmanship/kayak_materials/
The first Cayugas were made of this material, which I found was superior to the current soft, thin plastic Old Town is now using on the Cayugas. I did in fact notice an insulating effect of the triple layer.
With a lot of searching you can still find some Cayugas made of triple layer. The Old Town website says, "Currently, you will find it on the Twin Heron, Loon 111, Dirigo Series and the Camden Series."
It can be recognized by its harder, shinier surface compared to single layer, and by the tiny black flecks in the finish. It's an attractive, stiff material. Care needs to be taken not to puncture it. In my opinion and experience, the foam core will absorb water in the outer layer is punctured. This isn't really a big concern as it's a durable material. Mine was punctured not by paddling, but by a garage mechanic who overtightened the bow and stern straps, cracking the stern. It gained about 10 lbs after that.
I find that mukluks with heavy socks provide good warmth. Also, using a half or full skirt will help a lot. If a full skirt doesn't appeal to you, a half skirt will still be effective, much better than without it.