What is spray Foam insulation?

Spray foam insulation (SFI) is a mix of liquid chemicals that expand into a foam when sprayed into position, where it sets into an insulating layer. It has been used in the UK for over 30 years and is gaining popularity as an insulator that also helps improve airtightness. There are more than 40 manufacturers of SFI, some using gas propellants (the gas given off after the insulation has set is usually harmful to the environment, and possibly people). Others use soy or vegetable oil as the propellant. The manufacturer Icynene is unique in using water.

There are two types of spray foam insulation: closed cell and open cell. Closed cell is more like conventional rigid foam insulation boards, in that it is rigid once it sets and can offer some structural stability, but it does not allow air or moisture to pass through it. Icynene is the clear market leader in SFI and spends a lot of time lauding the benefits of its open cell structure. Open cell is more flexible and, because it adheres to the material it is sprayed onto, will tend to move with that material as it expands and contracts. It also allows air and moisture to move through it, giving it an almost ‘breathable’ quality. Whether it is actually a breathable insulation, like hemp, sheep wool or wood-fibre, is still open to discussion.

predominantly new build. The majority of new build in Scotland is timber frame and spray foam does an excellent job for them.” He added that the ideal situation was a 140mm stud wall where 120mm of insulation is sprayed in. This leaves a gap for pipes and cable and eliminates the need to trim off any excess.