Insulation works by slowing conductive and convective heat flow, while radiant barriers and reflective insulation reduce radiant heat gain through reflective surfaces in contact with air spaces.
R21 insulation is approximately 5.5 inches thick. This type of insulation is often used in walls and provides a higher R-value compared to standard insulation options, contributing to improved energy efficiency and thermal comfort in residential and commercial buildings.
Insulation typically lasts 20 to 30 years, though some types, like fiberglass and rockwool, can last up to 50 years.