Does fiberglass really loose some R-Value when its cold?
The quickest answer is Yes. Both cellulose and fiberglass insulation looses some R-Value when negative temperatures get extreme. There are the three types of heat loss: Convection, Radiation, and Conduction. They all play a role in your homes heat loss, but your attic insulation does its best job with convective and conductive heat loss. As it gets colder, your convective heat loss will increase at a faster rate as the warm air in your home gets into your attic. This is why its so important to also seal any air penetrations into your attic. In modern homes this is done very well with a properly installed vapor barrier. In older homes, this can be an issue that should be addressed. Effectively both products do not have a straight R-Value to temperature line, and their effectiveness’s have a declining curve. Because cellulose is denser, it is less subject to this R-Value loss, than fiberglass of the same depth. That is why the manufacturers recommendation for fiberglass requires a deeper
