Insulation materials are rated based on this R-value and the higher the value the longer it takes for heat to move through the material. In cold weather, insulation reduces heat loss, and in warm weather it slows the loss of the homes cooler temperatures and prevents a furnace from overworking. This greatly increases comfort, reduces sound, and reduces energy costs. For insulation to be effective it must be the proper type and have adequate thermal resistance for the homes location. Lastly it must be properly installed.
Most building codes specify the minimal amount of insulation and installation guidelines.
Since the mid-1970's insulation of new homes has been standardized. Walls adjacent to unconditioned spaces. Floors above unheated crawl spaces, basements and garages. Perimeter of slabs. Ductwork and piping in unconditioned areas.