Urea formaldehyde foam insulation is injected as a mixture of urea formaldehyde resin, an acidic foaming agent, and a propellant, such as air. It was commonly used in existing houses by injecting the foam into areas, such as behind walls, where it was impractical to provide conventional insulation. The insulation was approved in Canada for use in exterior wood-frame walls only.
Some formaldehyde gas is released during the on-site mixing and curing.
Formaldehyde is colourless, but has a very strong odour, which can generally be detected at concentrations above one part per million. It is this by-product of the curing of the foam that became a controversial issue. Formaldehyde is both a naturally occurring chemical, and an industrial chemical. It is found in dry cleaning chemicals, paper products, no-iron fabrics, diapers, pillow cases, the glue in particle board and plywood, cosmetics, paints, cigarette smoke, and the exhaust from automobiles, gas appliances, fireplaces, wood stoves. It occurs naturally in forests and is a necessary metabolite in our body cells.