Q.

What is the best material to use to patch Icynene spray foam insulation? Sometimes it’s necessary to remove a substantial amount of the stuff after it has been installed.

A.

David Ballantyne, project engineer at Icynene, Inc., responds: The best way to patch a hole in Icynene insulation will depend on the size of the repair. For small and medium-sized patches, a can of spray urethane foam (one-component foam from the lumberyard or hardware store) works very well. There is no compatibility problem with using other foam insulation products directly against Icynene. However, a large patch would require many cans of one-component foam, so it would be better repaired by installing more Icynene, or another two-component foam product applied by a professional applicator. Fiberglass batt insulation would be an option of last resort, since it will not be as resistant to air leakage as Icynene.