Styrofoam Insulation R Value
“Styrofoam” is a trademark of the Dow Chemical Company, and is used to refer to a variety of polystyrene-based products, several of which are commonly used for insulation. Styrofoam insulation R value can vary depending on a number of factors:
- Density: The initial density of the insulating material can drastically affect its resistance to heat transfer.
- Blowing Gas: The type of gas used to form the Styrofoam can be chlorofluorocarbon, carbon dioxide, air, or any number of other gasses.
- Handling: R value can be adversely affected by dents and chips in the surface of a rigid panel.
- Facing: Some Styrofoam insulation panels have a reflective surface on one side, usually a sheet or coating of aluminum. This foil not only serves as a radiant barrier, but it can also make a panel resistant to moisture.
- Installation: Incorrectly installing a Styrofoam insulation panel, or using it for any unintended purpose, will likely have a negative impact on the Styrofoam insulation R value.
Styrofoam comes in two common varieties: molded and extruded.
Expanded Styrofoam (molded expanded polystyrene, or MEPS) is made by bonding polystyrene beads together to form rigid boards. Expanded Styrofoam is white (and is, in fact, what most consumers think of when they use the term “Styrofoam”). It is most commonly used as a packaging material, but many people use it for insulation, even though it was never designed for that task. Depending on its density, expanded Styrofoam can have a Styrofoam insulation R value ranging from R-3.20 to 4.00, which is adequate for most insulation needs (comparable to fiberglass). However, expanded Styrofoam has a nasty habit of absorbing and holding moisture, which can lead to problems with mold, mildew, and rot.
A better bet for insulation is extruded Styrofoam (extruded expanded polystyrene, or XEPS). Extruded Styrofoam is formed by combining polystyrene crystals with additives and a blowing agent in an extruder. These ingredients are melted, and the liquid is pressed into insulation boards. Specifically designed for thermal insulation, extruded Styrofoam is waterproof and requires no air gap, meaning it can be tightly packed into a smaller space. Depending on its density, extruded Styrofoam can have a Styrofoam insulation value ranging from R-3.60 to 5.00.