Spray-on, also known as expanding foam, is one of several forms of plastic polymers, most commonly polyurethane and polyisocyanurate, used for the application or augmentation of building insulation.

 

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If applied correctly, spray-on insulation is nearly impervious to moisture, water and mold due to its closed-cell structure. This property also makes sprayed foam a popular choice in sealing large gaps within walls against air or moisture infiltration. If needed, cured foam can be cut, shaped and painted.

Polyurethane foam is sold by home centers and hardware stores in spray cans for consumer use. Long pants, sleeves, gloves, eye protection and good ventilation are strongly recommended. Polyisocyanurate products require specialized equipment and knowledge to install, and are thus sold only to trained professionals.