Building insulation is any object in a building used as insulation for any purpose. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation (e.g. for vibrations caused by industrial applications). Often an insulation material will be chosen for its ability to perform several of these functions at once.
Insulation is an important economic and environmental investment for buildings. By installing insulation, building use less energy for heating and cooling and occupants experience less thermal variability. Retrofitting buildings with further insulation is an important climate change mitigation tactic, especially in geographies where energy production is carbon intensive. Local and national governments and utilities often have a mix of incentives and regulations to encourage insulation efforts on new and renovated buildings as part of efficiency programs in order to reduce grid energy use and it's related environmental impacts and infrastructure costs.