What are the different types of insulation and their effectiveness?

Insulation slows the flow of heat through walls, attics and floors. Its effectiveness is measured as R-value: the higher the number, the better it resists heat flow. R-value depends on the material and the thickness, but also on how well it is installed. A gap or a compressed batt can lose a large share of its rated performance.

The main types

Fiberglass batts and rolls The most common type in US homes, sold in widths that fit between studs and joists. Roughly R-3 to R-4 per inch. Cheap and DIY-friendly, but it must be cut carefully around wires and pipes. Wear gloves, long sleeves and a mask.

Mineral wool (rock wool) Similar to fiberglass in form, slightly higher R-value per inch, denser, and naturally fire-resistant. It also helps with sound. Good for walls between rooms and near heat sources.

Loose-fill cellulose Made largely from recycled paper treated with fire retardants, blown into attics or dense-packed into closed walls. Around R-3.5 per inch. It fills irregular spaces well and is a common choice for topping up attic insulation.

Loose-fill fiberglass Also blown in, often in attics. Lighter than cellulose, so it needs a greater depth to reach the same R-value.

Spray foam Sprayed as a liquid that expands. Open-cell foam is about R-3.5 per inch; closed-cell foam is about R-6 to R-7 per inch and also acts as a vapor and air barrier. It seals air leaks very well but is expensive and needs professional installation.

Rigid foam board Polyisocyanurate, extruded polystyrene (XPS) and expanded polystyrene (EPS) panels, roughly R-4 to R-6.5 per inch. Used on basement walls, under slabs and as continuous insulation outside the wall framing.

How much do you need?

Recommended levels depend on your climate zone. ENERGY STAR and the Department of Energy publish recommended R-values by region; attics in cold climates often call for R-49 to R-60. The attic is usually the easiest and most cost-effective place to start.

Air sealing comes first

Insulation does not stop air. Gaps around pipes, wires, attic hatches, recessed lights and rim joists let warm air escape, carrying moisture with it. Seal them with caulk and spray foam before adding insulation. ENERGY STAR’s Save at Home pages explain how to approach both.

Safety notes

Older homes may contain vermiculite insulation (gray-brown, pebble-like), some of which contains asbestos. Do not disturb it; have it tested. Keep insulation clear of chimneys and of recessed lights that are not rated for contact.

Insulation is the base of every energy plan, as explained in the best ways to save energy at home.