Home Insulation Types and Where Each One Actually Belongs

Fiberglass batts are the most widely recognized insulation material in American homes, and for good reason. Pre-cut to fit standard 16- or 24-inch stud spacing, they slide neatly into open wall cavities, floor joists, and attic floors with minimal tools. R-values typically range from R-11 to R-38 depending on thickness.

They perform best in dry, enclosed cavities where they won't be compressed or exposed to persistent moisture. Compression significantly reduces their effectiveness — a batt rated R-19 stuffed into a space designed for R-13 will underperform both. Always install batts at the correct thickness for the cavity depth, and use faced batts (with kraft paper or foil) when a vapor retarder is needed, particularly in cold climates.

Attic floors are a strong application: lay batts between joists, then run a second layer perpendicular across the top for continuous coverage. Avoid using standard batts in basement rim joists or areas prone to humidity without additional protective measures.

Blown-in insulation — available in fiberglass or cellulose — is installed using a blower machine that allows the material to settle into irregular cavities, around obstructions, and over existing attic insulation without major disruption. Cellulose, made largely from recycled paper treated with fire retardants, is particularly popular for topping up existing attic insulation.

This material excels in open attic decks, enclosed existing walls via drill-and-fill methods, and floors over unconditioned spaces. Because it conforms to whatever space it fills, it covers gaps that batts would bridge over — reducing hidden air leakage points. Settling over time is a real consideration: cellulose can settle 15–20%, so installers typically add extra depth to compensate.

Renting a blower machine from a home improvement retailer is feasible for attic applications, but drill-and-fill wall installations require more skill and are often better left to experienced contractors to avoid inadequate coverage.

Spray polyurethane foam (SPF) comes in two main types: open-cell (lower density, vapor-permeable, around R-3.5 per inch) and closed-cell (denser, moisture-resistant, around R-6 to R-7 per inch). The key advantage of either type is that it expands on contact, sealing air gaps and providing insulation simultaneously — something no other material does as thoroughly.

Closed-cell spray foam is particularly well-suited for basement rim joists, crawl space walls, rooflines in conditioned attics, and areas with moisture exposure risk. Open-cell foam works well for interior wall cavities when air sealing is the primary goal and vapor management is handled separately.

Important: Professional-grade two-component spray foam involves chemical off-gassing during installation. Licensed insulation contractors use proper protective equipment, and occupants should vacate during application and follow re-entry guidelines provided by the installer. Small single-component cans are fine for sealing gaps around pipes and windows, but large-scale applications require professional handling.

Rigid foam boards — including expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate (polyiso) — offer consistent R-values (roughly R-3.8 to R-6.5 per inch depending on type) without the air gaps inherent in batt installations. Because they're solid panels, they can be cut precisely and layered to achieve target R-values.

These boards are the insulation of choice for exterior foundation walls, under concrete slabs, exterior wall sheathing, and basement interior walls. XPS performs especially well in below-grade applications where moisture contact is likely, as it resists water absorption better than EPS. Polyiso boards are common on rooftops and exterior sheathing applications but can lose some rated R-value in very cold temperatures — a factor worth discussing with a contractor in northern climates.

When installing rigid foam on basement walls, local fire codes typically require covering it with a thermal barrier such as drywall. Verify requirements with your local building department before leaving rigid foam exposed.

Mineral wool, sold as rock wool or slag wool, is manufactured from natural rock or industrial slag spun into fibers. It shares the batt format with fiberglass but offers meaningful performance differences: it is naturally fire-resistant (standing up to temperatures above 1,000°F), hydrophobic (it sheds water rather than absorbing it), and provides slightly better soundproofing than comparable fiberglass batts.

These properties make mineral wool well-suited for garage walls adjacent to living spaces, utility rooms, areas around fireplaces, basement walls, and any location where moisture intrusion or fire spread is a concern. Its density also gives it a slight edge in soundproofing between floors and rooms — useful in multi-story homes or home office conversions.

Mineral wool batts are typically denser and easier to cut cleanly than fiberglass, and they hold their shape without support during installation. R-values are comparable to fiberglass batts at the same thickness, so application zone — not thermal performance differences — is usually the deciding factor when choosing between the two.