Fiberglass has long been one of the most common types of insulation. It comes in many different forms, but the basic concept is that glass is heated and spun to form tiny fibers that stick together haphazardly. The structure traps air well, making it a good insulator.

Fiberglass Blankets

Fiberglass blankets can be made of batts or rolls. A batt is a form of insulation that looks like a carpet made of cotton gauze. Batts can be made of many different materials, and they come in various precut sizes. Rolls are made of the same material as batts, but they are rolled in on themselves like a carpet would be, and they are designed to be cut to the size you desire.

Standard fiberglass blankets have R-values between 2.9 and 3.8 per inch. This means in a house frame with 2″x4″ studs, you will be able to accumulate an R-value of between 12 and 15. Current energy standards recommend an R-value of 18 for exterior walls in homes in Pennsylvania’s climate zone, so if you have a 2″x4″ frame, you should consider new, higher-density fiberglass blankets. They are more expensive, but they will keep your house warmer so you will save money on energy bills. Medium-density and high-density fiberglass blankets have R-values ranging from 3.7 to 4.3 per inch. If, however, your house frame has 2″x6″ studs, you may be able to achieve ideal R-values with standard-density fiberglass blanket.

For more on fiberglass blankets please visit: U.S. DOE site

Fiberglass Loose-fill

The other common form of fiberglass insulation is loose-fill. Many different types of insulation can come in the form of loose-fill. Its defining characteristic is that the material is shredded and usually has to be installed with a machine that blows it into the space you want to insulate. It works by trapping air in-between the little shreds of material, thereby preventing heat flow.

However, Fiberglass loose fill is a bit less efficient per-inch than fiberglass blankets, but loose-fill presents its own benefits. Most notably, because it’s loose it can fit in spaces that blanket may be too big or square to fill completely. It’s very important to keep this in mind, because air movement around insulation can significantly reduce insulation’s effective R-value.

Using the two forms of fiberglass in conjunction may be a good idea. You might have the majority of your building envelope lined with fiberglass blankets and use loose-fill to get at the nooks and crannies of your house frame.

Health Concerns

Both forms of fiberglass insulation present potential health concerns. Several health authorities have listed fiberglass as a possible carcinogen, although it is regarded as safe if it is installed and maintained properly.

For more on fiberglass safety, please visit: American Lung Association

Or this fact sheet from the Illinois Department of Public Health
For more information on fiberglass, please visit:

The North American Insulation Manufacturers Association

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