Spray Foam vs Fiberglass Insulation: Compare Complete Assemblies

Record whether the insulation belongs in cavities, across an attic floor or at the roofline. Specify total target resistance and the associated air, moisture and protective layers. A fiberglass batt order generally uses coverage packs or cavity pieces; a spray-foam order uses area and thickness or board feet.

Air sealing is part of the assembly scope, not a value automatically included in every material price. Avoid assuming that a batt pack includes a separate air barrier or that a foam category resolves every transition and penetration.

A 100 ft² cavity area can need three 40 ft² packs at zero waste, but the declared batt R depends on the exact product and thickness. The same area at a specified 2 in foam application represents 200 board feet. These quantities cannot be compared directly as numbers of packages.

For framed walls, compare complete thermal paths. Using a cavity label as whole-wall R ignores framing. The simple R-value tool can demonstrate a parallel-path difference, but it does not certify complex thermal bridges or moisture behavior.

Include substrate preparation, access, air sealing, application or fitting, protective coverings, trimming, disposal and tax. Use actual declared product properties and installation requirements. A lower materials-only subtotal may have a different preparation or finishing scope. Decide between suitable assemblies with matching project outcomes, then use the appropriate quantity engine for the purchase order.