How Cotton Insulation Contains Heat

Heat Conductors and Insulators

• Heat moves from objects that have a higher temperature to objects that have a lower temperature until they have the same temperature, which is called thermal equilibrium. However, some materials conduct heat better than others. Materials that conduct heat well, such as metal and diamond, are called conductors. Materials that don't conduct heat well, such as wood, plastic, polystyrene and down, are called insulators. Cotton is an insulator, so it helps your home stay warm or cool. By the same principle, cotton clothing helps you stay warm by conserving body heat.

Cotton Insulation Basics

• Cotton insulation comes in blankets, which can be installed on ceilings, walls and floors. Batts are precut sections of blankets, while rolls can be cut to fit a certain shape. Cotton insulation is typically made from 85 percent recycled cotton and 15 percent plastic fibers that have been treated with a flame retardant, according to Energy Savers. Cotton has an R-value, or thermal resistance value, of 3.4 per inch. The R-value of a material refers to its ability to slow heat transfer. Higher R-values slow the flow of heat better than low R-values.

Advantages

• Cotton is nontoxic, so installing cotton is safer than installing fiberglass blankets or other types of insulation. Cotton also employs recycled materials, so it is environmentally friendly. For example, some cotton insulation is constructed from wastes produced in the blue jean manufacturing process. The R-value of cotton is also higher than that of some other types of insulation, such as straw or loose-fill fiberglass, which have respective R-values of approximately 2.4 and 2.3 to 2.8 per inch.

Disadvantages

• Cotton is 15 percent to 20 percent more expensive than fiberglass batts, according to Energy Savers. Cotton batts also have a lower R-value than other types of insulation, such as extruded polystyrene, urethane and polyisocyanurate, which means cotton slows the transfer of heat less effectively than these materials. For example, polyisocyanurate has an R-value of 7.2 to 8.7 per inch. In addition, cotton and other types of batts and blankets are difficult to install in areas that have obstructions or in cavities. Loose-fill insulation may be more appropriate for these areas.