Cutting Rigid Insulation
Learn how to cut through rigid foam insulation like butter.
Foam insulation boards are high in R-value, but they can also be a nuisance to cut — especially foam boards that are 2 in. thick. A utility knife won’t cut deeply enough. A kitchen knife works, but not very well because the triangular cross section of the blade binds as the cut deepens. Saws leave rough edges and spew statically charged insulation particles that cling to everything.
A simple 2-in. putty knife, however, does a wonderful job of cutting foam insulation. The trick, as shown in the drawing, is to sharpen one side of the blade. Teamed up with a straightedge, a sharpened putty knife cuts through foam like butter, and its wide blade keeps the cut from wandering.
— Chris Ellis; Brewster, MA
From Fine Homebuilding #125
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Updated November, 2024.
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View Comments
There is a tool made for cutting foam that my one supplier sells that is made by Rock Solid, so sharp that I made a blade guard for when it is in my tool bag
It is the Insul-Knife by Rock Solid Tools, http://www.rooferschoice.com/catalog.asp
I just use a knife blade in my jig saw.
Simple, works on 2" foam, leaves no mess.