There are lots of ways to insulate a foundation, but as Joe Lstiburek reminds us in this recent BSC article, foundation insulation needs to be protected from UV, insects, and impacts. That's a tall order, and Lstiburek surveys several different methods and materials that can be used to meet this requirement. Among the options he mentions are cement board, cellular PVC (a detail that Minneapolis builder Michael Anschel also favors in his JLC article "Making Open-Joint Siding Work"), metal, and stucco. In some areas, foundations require a way to inspect the mudsill for termite damage, an important consideration that Lstiburek includes in some of his foundation insulation details. Builders looking for more guidance on specific products for foundation protection might be disappointed - for example, Lstiburek mentions 'stucco', but doesn't weigh in on the various types that are available for this purpose - but otherwise provides clear guidance on this important detail.