What makes Spray Foam so much better than conventional fiberglass insulation?
The biggest downfall of fiberglass insulation is that its Long Term Thermal Rating is substantially reduced over time. The numbers on a bag of fiberglass insulation (R-value) are very deceiving. When the bag says R20- it means that it will provide that rating if it is installed perfectly, without any air movement or gaps. The Long Term Thermal Rating of an R20 fiberglass batt is at best R12. This is because it will sag and gap for a variety of reasons (gravity, house shifting, pulling wires through wall space, vibrations in house, etc.) For every 1/8″ gap you will lose 40- 50% of the R-value. Spray foam insulation is guaranteed to never gap, sag or crack, while fiberglass insulation has no such guarantee.
