**People do use both rigid foam and spray foam in attics.** For a typical vented attic, though, fiberglass or cellulose usually offers a simpler, cheaper way to add insulation.

The key distinction is **where you insulate**:

- **At the attic floor:** The attic stays outside the heated/cooled space, and its vents remain open. Batts or blown insulation work well here. Spray foam also works; one established approach uses a thin layer of closed-cell foam for air sealing, topped with loose-fill insulation. [PNNL attic-floor guidance](https://basc.pnnl.gov/resource-guides/spray-foam-insulation-applied-existing-attic-floor)
- **Along the roof’s underside:** Spray foam can bring the attic inside the insulated enclosure. This typically involves converting it to an unvented attic, insulating the gable walls, and providing humidity control. That can be useful when HVAC equipment and ducts are in the attic, but it requires a coordinated design. [PNNL roof insulation guidance](https://basc.pnnl.gov/resource-guides/below-deck-spray-foam-insulation-existing-roofs)

For your upgrade, foam has several tradeoffs:

**Rigid foam costs more and takes fitting work.** Cutting boards around joists, braces, and wiring takes time, and seams need sealing if the boards are to control air leakage. Boards are particularly useful for attic hatches and other localized applications. In a spacious attic, adding depth with loose-fill insulation is straightforward. [DOE Energy Saver guide](https://www.energy.gov/sites/default/files/2022-08/energy-saver-guide-2022.pdf)

**Spray foam needs careful preparation and installation.** Existing insulation and dust generally need removing from the surfaces being sprayed. Correct mixing, application thickness, and surface conditions matter. Foam also makes later access to anything it covers more difficult; electrical junction boxes must remain accessible. [PNNL attic-floor guidance](https://basc.pnnl.gov/resource-guides/spray-foam-insulation-applied-existing-attic-floor)

**Foam has fire and moisture requirements.** Exposed foam may need an approved ignition or thermal barrier, depending on the product, attic use, and local code. Roof-deck installations also need climate-appropriate vapor control to prevent moisture accumulating in the roof sheathing. Open-cell and closed-cell foam behave differently in this respect. [PNNL roof insulation guidance](https://basc.pnnl.gov/resource-guides/below-deck-spray-foam-insulation-existing-roofs)

**Assuming yours is an ordinary vented attic, I’d start by air-sealing the ceiling penetrations, maintaining clear ventilation paths at the eaves, and adding blown cellulose or fiberglass.** Blown insulation fits around irregular framing and can cover the joists continuously. Batts are also suitable if fitted carefully. [DOE attic air-sealing guidance](https://bsesc.energy.gov/energy-basics/air-sealing-existing-attics), [blown insulation guidance](https://bsesc.energy.gov/energy-basics/blown-insulation-existing-attics)

Check the recommended **total** R-value for your climate before settling on R-30; your location may justify more. [ENERGY STAR recommendations](https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values)