Spray Foam Insulation
One of the high-tech insulation products being utilized these days is a foam-spray product called "Icynene," which is a foam that starts as two liquid components (a and b, if you will) that are heated up and sent through two hoses and meet at a tip of a gun where the magic begins. This is a thin film that expands to 100 times its volume in eight seconds, when it's permanently set up.
During the installation of this particular spray foam the house begins to look like the set of a sci-fi movie, and protective gear is needed because the over-spray can be harmful to lungs.
After the product sets up it has a rough texture that expands beyond the drywall barrier. The installers have to "scarf" — scrape off — the foam in order for the drywall to fit properly. The installers basically make sure the foam is cut smoothly.
This particular foam insulation won't allow air to move through or around it, creating a complete air barrier. Icynene can also be applied to the underside of a roof deck, creating an airtight seal between the roof and the attic space.
Note: The practice of foam insulating the attic has raised eyebrows in the building industry because "standard" roofing techniques call for the attic to be ventilated; however, in a vented attic situation it will become approximately 130 degrees in the summer. There's no reason for an air-conditioning and vent-ductwork to have to work in that type of severe conditions. By applying Icynene right on the underside of the roof deck, the severe temperatures no longer exist in the attic. In short, the attic is now a "conditioned" space of the house that is just as comfortable as any other room in the home. This is called a "Compact Roof", which means you can frame right up against it. The one drawback of using expanded foam on the inside of the roof is that this will cause the temperature of the shingles to rise, but how much is not yet known. And how much damage a rise in temperatures could cause is debatable.