Icynene is a spray-on foam insulation that you can use to insulate a home. Typically it would be used during new construction because (as seen in the videos below) in needs to be sprayed on like paint before the sheetrock goes on. The advantages claimed for icynene include:

1) Higher R values (because it is uniform)

2) Much lower air infiltration from outside

3) Better sound insulating properties

4) Better moisture barrier

The claim is that it can reduce heating and cooling costs by as much as 50%.

These two videos introduce the product and show how it is applied:

Are there any problems with icynene? The comments below are enlightening and you should read through them, since they discuss outgassing problems that have been experienced by several Icynene customers. See also this cautionary tale:

How Sensitization Works – becoming “allergic” or “sensitized” to common chemicals can be a nightmare

There is also this:

- Icynene Dangers and Problems

After reading it, one thought I had was that water leaking into any wall cavity insulated with anything (including fiberglass) will cause mold. But the points made about getting the stuff out if you ever need to are interesting. If you were to ever need to remove icynene for repairs or renovation, it would be a major headache (especially around wiring and pipes).

For more info see:
- Icynene.com
- Icynene FAQ
- The Icynene Insulation System®: An Introduction
- Spray foams (insulation) (discusses differences between open cell foam and closed cell foam)
- How to Identify Icynene® Foam Urethane Foam, Isocyanurate Foam Building Insulation Products & Their Properties