Urea formaldehyde foam insulation (UFFI) was a very effective material for improving the wall insulation of existing homes during the late 1970’s. It could migrate inside walls to fill voids far better than other materials when thin insulation was already present in walls.
Sometimes, particularly if formulated improperly, the UFFI would give off formaldehyde gas, especially during hot and humid weather. Formaldehyde gas is an irritant and even potential carcinogen. UFFI was therefore banned in 1982 and is no longer used.
Even though old UFFI may still to off-gas during prolonged hot and humid weather, the formaldehyde off-gassing 35 years later is less than from the cabinetry, carpets and subflooring in newer homes. If UFFI is discovered during your home inspection, consider installing central air conditioning to control hot and humid conditions.