Skip to main content

Fiberglass Insulation

The knowledge of the physical characteristics of the various insulations available can be useful to homeowners in deciding which kind to use. Especially in the North, where large temperature differentials exist across outside walls, ceilings and floors, the knowledge can be put to good use. Important characteristics include thermal resistance (R-value or K-factor), water absorbency, strength, change with age, flammability and toxicity under normal temperature and when burned.

Fiberglass, an old insulation standby, had its first beginnings in ancient Egypt when people discovered they could draw hot glass into threads which were placed around vessels for decoration. The modern technique of making fiberglass insulation, developed in 1931, involves jetting of molten glass through tiny heated holes into high-speed air streams wherein the resulting fibers are drawn very thin and to great length. Enough glass to make one large marble forms about a hundred miles of single fiber. Multiple fibers are collected into a matte which is the end product.

Made from sand (SiO 2 ), limestone (CaCO 3 ) and sodium carbonate (Na 2 CO 3 ), fiberglass is inert, ages well, does not burn and does not emit toxic gases except when in a hot fire. Even then, there is less emission than from wood or any other common insulating material. Fiberglass does not take up water within the glass fibers, but water passes freely between the fibers. Therefore, fiberglass insulation must be used in conjunction with a vapor barrier placed on the inside, toward the heated room.

Fiberglass in batts has a R-value per inch thickness of about 3.1 and costs (in Fairbanks) about six cents per inch-thick square foot. As blown insulation, it has a slightly lower resistance to heat loss (one inch R-value about 3.0) but can be purchased installed for about seven cents per inch-thick square foot. Thus, except for blown cellulose insulation which costs about the same, fiberglass in batt or blown form is the cheapest insulation on the market for the insulating value achieved. Of course, for certain applications, other more expensive insulations are more desirable.