Foam Board Insulation vs Fiberglass: In-Depth Comparison

Foam board insulation is a lightweight rigid board, usually 4-by-8-foot in dimension. The chemical makeup of these boards varies from polystyrene (EPS or XPS) to polyisocyanurate (polyiso or iso). Foam boards are formed by chemically altering these plastic resins, heating and expanding the material to create air pockets.

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Here are some quick comparisons of foam board types:

• Extruded Polystyrene (XPS): Unfaced foam boards

• Expanded Polystyrene (EPS): Unfaced foam boards

• Polyiso (iso): Foam core with facers on both sides

Installation of Foam Board Insulation

Foam board insulation can be installed in a variety of ways, including loose-laid, mechanically fastened with screws and plates, or glued to a substrate with adhesive. Common applications of foam board insulation include: slabs, basement walls, exterior walls, and roofs. The modular dimensions of foam board insulation make it easy to fit these boards together, creating a continuous insulation application.

Fiberglass Insulation Types

Unlike rigid foam boards, fiberglass insulation is flexible and soft. This insulating material is made from spun fiberglass and binders and it comes in loose-fill or rolls or batts that are sized to fit between stud and joist cavities. Fiberglass rolls and batts are available faced with kraft paper or unfaced.

Installation of Fiberglass Insulation

Fiberglass is made to fit inside wall cavities. Paper-faced fiberglass can be stapled to wood framing to hold it in place. Since it is soft and flexible, fiberglass insulation must be secured to and supported by surrounding framing when installed. It loses some of its thermal insulating value when compressed, so it needs to remain fluffy and not in compression. Loose-fill fiberglass insulation requires professional installation and special equipment.

Comparing R-Value Performance

When comparing foam board insulation vs fiberglass, thermal performance is a key factor to evaluate. The thermal performance of insulation is measured in R-value. A higher R-value means that the insulation performs better at reducing heat loss through it. Polyiso has an R-value of R6 per inch, while fiberglass has an R-value of less than R4 per inch.

R-Value of Insulation by Type