I'm sure that you've all heard of fiberglass in insulation. If not, recall a commercial of a pink copyrighted cat of some sort that was the spokesman for a certain type of insulation.. ring a bell? Pink something or other.
Fiberglass is an old insulation standby, and 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 (SiO2), limestone (CaCO3) and sodium carbonate (Na2CO3), 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 little. As blown insulation, it has a slightly lower resistance to heat loss (one inch R-value about 3.0) but can be purchased installed more cheaply 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.