Spun glass fibers made just like cotton candy only at 2000 degrees.
- Essentially non-combustible.
- Fairly inexpensive.
- Sold everywhere. 30-40% recycled, the rest is sand which is a rapidly renewable resource.
- Decent R-value/inch.
- Does not absorb moisture.
- Will not support mold/fungus.
- Can perform very poorly if air can blow through it, which happens in attics and often inside walls that are poorly sealed.
- Loses substantial R-value as temperature falls, approximately 20% at 30 degrees and 50% at -20 degrees. Slightly more expensive than cellulose.
- Diminished R-value due to thermal bridging.
- Does not prevent radiant heat transfer – the primary source of heat-flow in and out of buildings.
- Pinching, smashing and thermal bridging reduces its R-value.
- Moisture reduces its R-value.
- Potential health risks such as lung damage.
- Batts do not seal wall and ceiling cavities tightly.
- Needs an additional vapor barrier to protect it from moisture.
- Can settle resulting in declined effectiveness.
- Moisture build-up between the fiberglass and the building exterior cannot evaporate, therefore causing mold, mildew and decay.