Spray-foam has a reputation of providing superior insulating qualities compared to fiberglass batt, mineral wool, cellulose, and other insulation alternatives.
The truth is that spray-foam does not necessarily perform better than other types of insulation when it comes to conductive heat transfer. Think about the insulation products you’ve seen at your local home-improvement store. Remember that big number on the label that started with an ‘R’ (the roll of batt insulation might have read R-13, for instance)? That number identifies the thermal resistance value – or R-value – and it is used to communicate the rate of heat flow through a material. The greater the R-value, the smaller the rate of heat flow (but beware, this is not a linear relationship).
Inch-per-inch, the R-value of spray-foam insulation is not much different than some other common alternative insulation options. Spray-foam helps a structure perform more efficiently because it reduces another form of heat gain/loss – air leakage.