Cavity Insulation
Cavity insulation is the insulation installed inside the framing cavities of a wall, ceiling, or floor — between the studs, joists, or rafters. It is the cheapest way to get bulk R-value into an assembly because the frame already exists. Common cavity insulation includes fiberglass batts, mineral wool batts, dense-pack cellulose, and open-cell or closed-cell spray foam. The downside of cavity insulation is that it does not break thermal bridges through the framing — which is why Passive House and high-performance builds always pair cavity insulation with continuous exterior insulation.