Doors and Windows - Foam or fiberglass insulation???

what is the advantage of using low expanding foam insulation rather than fiberglass insulation? is foam water resistant and fiberglass is'nt?

Too much to describe in the format, suffice it to say that each has its' approriate usage. There are two main types of expanding foam, open cell and closed cell. What is correct for your application takes a local expert. Installing the wrong type can cause major damage. What is correct for one climate is not right for another.

The foam tends to be an air barrier as well as an insulator, where fiberglass does not stop the flow of air. But that is part of what Bill was saying. With some air movement, things can dry out. Seal it up in the wrong manner and you can trap the moisture. If you are confident the window and everything above it is flashed properly, I would go with a zero expansion or low expansion foam. If you use a low expansion, don't try to fill deep cracks all at once, try 50/50. You can also fill the gaps 80% with fiberglass and then the final inch or so with foam.

For the most part, I just use the can stuff from the big boxes. For zero expansion I use Dap.

Bud

can fiberglass alow mositure in causing mold? foam is better as a water barrier? does it allow water vapor to breath?