Insulation is material installed in buildings to reduce heat transfer between interior and exterior, maintaining comfortable temperatures with less energy. Common insulation types include fibreglass batts, cellulose (blown-in), spray foam, and rigid foam boards. Insulation is measured by R-value—higher R-values indicate better insulating performance. Building codes specify minimum insulation requirements for different climate zones and building components (walls, attics, basements). Adequate insulation reduces heating and cooling costs, improves comfort by reducing drafts and cold surfaces, and lowers greenhouse gas emissions from reduced energy consumption. Many older buildings have inadequate insulation by modern standards—upgrading insulation is among the most cost-effective energy efficiency improvements. For municipal buildings, insulation improvements reduce operating costs and support climate action goals. Insulation retrofits are commonly supported through utility rebate programs and government energy efficiency incentives.