Cotton insulation was originally developed as a non-irritating alternative to fiberglass using virgin cotton. Now it is made from approximately 95% post-industrial recycled fiber — from recycled bluejean waste — so the insulation has an indigo bluejean color.

The cotton is actually 25% polyester fibers, which improves tear strength and recoil characteristics.
Demand for this product has grown. It comes unbacked or backed with Kraft paper. It also comes in loose form for blow-in applications. Its rating is in the range of R-11 to R-19 and comes 3–1/2” and 5-1/2” thick. Its cost is from 20¢ to 50¢ per square foot.
Although a favorite among environmentalists, there are just a few concerns with cotton insulation. Early fire safety issues necessitated substantial treatment with boric acid (or Borate), a fire retardant. Other products use aluminum sulfate for fire protection. If moisture is present, aluminum sulfate can corrode steel or copper (such as in fasteners or plumbing) that might come in contact with the insulation. Borate is non-corrosive.
Cotton dust has the potential for some respiratory irritation during installation. Those who are chemically sensitive may have concerns with the indigo dyes and the residue from pesticides used on cotton crops, which are the most heavily sprayed crops in the world. Still, it is recommended for use by many chemically sensitive people.
Batt insulations may be an absorbant for VOCs. Use of an impermeable membrane, called a vapor barrier, can cover the insulation and assist in resolving this problem. During installation, care should be taken to avoid compressing this material which could effect its insulating ability.