Cellular vinyl windows

I'm just curious... how many companies out there are manufacturing vinyl windows out of cellular vinyl? What are the advantages / disadvantages of the product over standard vinyl? Have you actually seen, sold or installed cellular vinyl windows? And what is your opinion of them?

Amsco is making a good one. It has better energy rating that standard vinyl, it cuts like wood, melts like vinyl. So it is rigid and can have a solid fusion welded frame. Looks really good, just cost more.

Thanks, but their website seems to indicate that they are made of a composite material, containing wood fibers. Cellular vinyl is similar to the stuff that vinyl brickmould is often made of. It's like vinyl whipped with air to make it lighter, with more insulating properties. http://www.marleymouldings.com/wd/cellular.html