Blown-in insulation has long been a favored method of filling the gaps in existing structures, but new cementitious foam goes the extra mile by providing a fire-resistant, non-toxic barrier with improved insulating properties.

Cementitious foam is made entirely of magnesium oxide and air. It is blown through a membrane with air, resulting in a continuous network of mineral surrounding bubbles of air.

While it will require a professional to actually blow the insulation in, you can help reduce the time and cost of set-up by helping prep the area that needs insulation. The insulation is thick enough to be retained by almost any netting, screening, or chicken wire, or it can be foamed in behind house wrap or polyethylene.

There are two things to pay attention to when prepping the area and hanging the membrane that will contain the insulation.

First, the membrane must be installed tightly against the wall studs to avoid "pillowing," which can create an uneven surface and complicate drywall attachment. To avoid this, try stretching the netting very tightly or applying a coat of glue through the netting to secure it continuously to studs. If you are using polyethylene as a containment membrane, try stretching it hand tight and applying frequent inset stapling.

The second issue is that a vent will be needed to allow air to escape ahead of the filling insulation. If you are using chicken wire or netting, this isn't a concern, but in air-tight membranes you will want to slit a small vent to allow air to flow out of the filling space. Once the insulation is installed, you can seal the air vent.