A sectional door insulation system has one or more insulation blocks attached to a protective sheet. Small grooves between the insulation blocks and the protective sheet accommodate brackets on the lower and upper walls of the section of a door, such as a garage door. The secure engagement of the brackets of the door and grooves of the panel holds the panel firmly attached to the door section. The protective panel may have a textured surface. The insulating block may optionally include a barrier foil and tabs.