Attics contain cold air in the winter and hot air in the summer. Insulation in the attic is what keeps the hot or cold air contained. Insulation is rated by its R-value or thermal resistance. The thickness of the insulation does not affect its R-value. The value is determined on how well it contains thermal air. Proper R-value insulation will prevent hot air from entering the home in the summer and escaping in the winter. Thermal resistant insulation is rated by numbers. A higher number means a better insulating quality.
Heat will transfer by convection which is hot air rising. Conduction heat is a source such as the sun heating the roofing material and conducting it into the attic. Then there is radiant heat that is the transfer of heat from one place to another. Proper insulation in the attic will prevent these types of heat transfers.
Reflective radiant heat barriers can be used in the attic along with thermal resistant insulation. The reflective barriers come in thin sheets that can be stapled to the roofing trusses. The barrier will reflect back out of the attic the radiant heat. Homes in the wintertime of course run their heat. The hot air in the home will rise and if there is no thermal resistance the heat will be lost. Good attic insulation will prevent the heat from escaping in the winter. The insulation in the summer blocks radiant heat from entering the house.The hits keep comin’: Definition: Insulation