Insulation is the process of keeping heat within a property, usually by covering areas exposed to the outside, such as roofs, floors and walls.
Without it, indoor temperatures are difficult to maintain, and homes can lose up to 45% of their heat, according to the Energy Savings Trust. This means that heating needs to be left on for longer to maintain a comfortable temperature.
The UK has some of the least energy-efficient housing in Europe and even newer homes may not be properly insulated.
If the temperature drops quickly once the heating goes off, the home is unlikely to be properly insulated.