Types of insulating materials
There are four traditional types of materials used in home insulation.
Cellulose is basically recycled paper that is treated to resist pests and fire. It is typically blown loosely into attic spaces or combined with a glue/water mixture and blown into walls. The main advantage of this material is that it is the least expensive. A disadvantage is that it has a high rate of settling (typically 20%). Therefore, it can lose a significant part of it's R-VALUE over time. Another disadvantage is that, when it is blown wet into the walls, time is required before covering it with drywall so that it can dry out. If this is not done, mold and other indoor air quality issues can occur.
Fiberglass is the most common material used in home insulation. Although it is more expensive, it tends to settle less (typically only 1-3%) and therefore it retains it's R-VALUE better and longer than cellulose. Another advantage is that, the material does not retain moisture like cellulose. Therefore, if the material becomes wet, it will dry out and return to it's original R-VALUE. The product is available in blankets which are long rolls that can be cut to a desired length. Blankets are typically used in attics. When these blankets are precut into lengths that fit into wall spaces they are referred to as batts. This material is also available in bags for loose fill. This is typically blown into attics with a machine. (The machine is avaialable for rent at most home centers.) An advantage of this form is that it can fill in hard to reach areas.
Foam is another material commonly used for home insulation. This is available in rigid board form which can be used on the exterior of a home, basement walls, or walls in an unconditioned crawlspace. The spray foam (polyisocyanurate) is a combination of a resin, hardener, and air. It is typically mixed on site and blown into walls and attics. The main advantage is that the material expands when applied and is good at making an air barrier. The product also does not settle and is not affected by moisture. The main disadvantage is it is the most expensive.
The final material is known as a radiant barrier or reflective insulation. This is typically an aluminum foil that is incorporated with a foam board or a bubble wrap type material. Unlike the other materials, this product reflects infrared heat. This material is normally used in attics and on hvac ducts.