Loose-fill insulation
Loose fibers are blown across an attic floor through a hose. Cellulose is largely recycled paper fiber treated for fire and pest resistance; fiberglass loose-fill is made from glass fibers. Both flow around many obstructions better than a hand-cut batt, which is why they are common for attic top-ups.
The installer must meet the product label's minimum bag count and installed depth for the promised R-value. Depth alone is incomplete because too little material can be fluffed to look deep, then settle below the intended density.
Batts and rolls
Pre-cut batts and long rolls fit regular framing bays. Fiberglass is common and relatively light. Mineral wool is denser and handles high temperatures well, though product cost and availability vary. Either material loses effectiveness when squeezed behind wires, tucked loosely around bracing, or cut with open gaps.
A second layer can cross the joists and reduce thermal bridging when the attic will not be decked for storage. Keep eave ventilation paths open with baffles where the roof design requires them.
Foam products and hybrid assemblies
Open-cell and closed-cell spray foams insulate and resist air movement, with different vapor behavior and R-value per inch. They are often considered when the thermal boundary moves from the ceiling to the roof deck. That change affects attic temperature, roof drying, HVAC loads, and combustion safety.
Rigid foam boards appear in attic hatches, knee walls, and some exterior roof retrofits. Hybrid assemblies combine materials, but every layer should have a clear job. More material types do not automatically produce a better roof.
Primary sources
Product details, health guidance, and code references were checked against these sources.
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