Whether retro-fitting a home or choosing insulation when building a new one, homeowners are learning that spray polyurethane foam (SPF) insulation is a great way to save on energy costs and improve comfort. It is a spray-applied cellular plastic that forms a continuous barrier on walls, around corners and on all contoured surfaces. SPF insulation applied by professionals is generally described as a high pressure foam or a low pressure foam and is available as "open-cell" or "closed-cell" foam. There are several major differences between the two types, leading to advantages and disadvantages for both, depending on the desired application requirements. It is important to discuss with your contractor which type of SPF insulation may be best suited to your application. A side by side comparison highlights some of the typical differences between closed-cell and open-cell foam.