We chose Quad-Lock forms because it gave us the ability to increase the R-value over standard ICFs. Whereas wooden forms are removed (and reused) after the cement wall is poured and hardens, the Quad-Lock forms stay in place and serve as insulation (unlike most homes, our crawl space is insulated). Here you can see the 4 1/4″ outer wall and the 2 1/4″ inner wall, yielding R-3o.Usually, the forms for a foundation wall are made using wooden forms, but we used Quad-Lock ICFs (insulated concrete forms). They’re made of expanded polystyrene and look a lot like Legos.
This post is an excerpt from http://skip-and-bettys-place.blogspot.com