"Ceiling insulation tends to make the most measurable difference to interior temperatures, it's so effective that it's been made a legal requirement for all newly-built homes and extensions in South Africa," says Clarke. There are several types of ceiling insulation available on the market, but make sure to check the thermal resistance value, or R-value, of your chosen product to ensure it's appropriate for your home and climate. The higher the R-value, the more insulation the product provides.