Why Is Styrofoam a Good Insulator?

By Max Roman Dilthey; Updated April 24, 2017
Close-up of styrofoam

Styrofoam, or polystyrene foam, is a petroleum-based plastic foam with exceptional insulative properties. Styrofoam is 95% air, allowing it to trap warm air and prevent heat loss when used as insulation in a building or a disposable coffee cup. The trapped air inside the Styrofoam prevents heat from effectively passing out of your home, making your heating system more efficient. Styrofoam extruded polystyrene home insulation has an R-value of 4.0 per 1 inch thickness, making it better than some insulation like fiberglass, but worse than closed-cell foam.

R-Value and Efficiency

According to Great Day Home Improvements, "R-value is a measurement of thermal resistance and measures the ability of heat to transfer from one side of an object to another." Styrofoam insulation's R-value is 4.0 per inch, compared to solid wood's R-value of 1.0 per inch. Fiberglass batting provides less insulation with an R-value of 3.14, while closed-cell spray foam provides a very efficient R-value of 6.5. Environmental differences like the heating system in your home, the location of your house, and the materials used in your home's siding and interior walls can all positively or negatively affect the insulating properties of your home, regardless of your insulation.

About the Author

Max Roman Dilthey is a science, health and culture writer currently pursuing a master's of sustainability science. Based in Massachusetts, he blogs about cycling at MaxTheCyclist.com.