Ever wonder what happens to all the scrap cotton denim that's left over when designers are making all of those blue jeans? Well some of that material actually gets recycled into insulation. Cotton is a natural and renewable resource, which makes the plant one of the greenest insulation products on the planet. Cotton insulation is similar to fiberglass insulation in several ways. For one thing, it can be rolled into batts. Additionally, the R-value of cotton insulation and fiberglass is the same, roughly R-3.2 to R-3.7 per inch of thickness [source: Build It Green].
However, unlike fiberglass, cotton insulation does not contain formaldehyde, which scientists have linked to some types of cancer [source: National Cancer Institute]. Cotton's fibers will not cause any respiratory problems. The material is very good at absorbing moisture, and when treated with boric acid, is flame retardant. Cotton insulation is also insect repellent. However, one of the drawbacks of cotton insulation is that it costs twice as much as fiberglass [source: Build It Green].