Insulation, Radiant and Vapor Barriers - Insulation under radiant floor heating tubing

I have a new home with radiant floor heating. The heating is PEX tubing under the floor held in place with aluminum defuser plates. I was told to install foil faced fiberglass beneath the heat tubing but can not find such a product.

I considered using foil faced rigid board (1" thick) but that is twice the cost of fiberglass and has less R-value. As a practical application I would like to use the fiberglass rolls that are encased in a plastic cover. This would work especially well in my workshop to stop the dust accumulating in exposed fiberglass.
However, the temperature of the fluid in the tubing runs between 120 and 140 degrees and I don't know if this would destroy the plastic covering. Any suggestions? Thanks:confused:

www.radiantec.com and click on pricing and then individual components. Scroll down and you'll see a product known as a radiant barrier. If you search the web, you'll see other manufacturers of radiant barriers and you might be able to get a better price. You staple this up against the pex tubing and then install you plastic encapsulated insulation under the radiant barrier.

In most towns where insulation is installed, it must be covered with a fire preventive material usually an hour rating. You should check with your local building code department. If you didn't have the workshop, the insualtion would not have to be covered.

I know Radiant Direct (http://www.radiantdirect.com/) sells barriers, you might want to try them.