Typically, the hottest time of year for Americans in the lower 48 states is during the summer months of July and August. Whether you’re doing hobbies, working in your garage, or even if your laundry appliances are there, it can be significantly hot. This is especially true since garage temperatures can be 10 to 18 degrees Fahrenheit warmer than the outside air.
One way to cool down is using a portable air conditioner. However, purchasing one has an initial cost, often hundreds of dollars, and it increases your electricity bill, particularly damaging for those in states with higher electricity costs. A more budget-friendly and eco-friendly alternative is to insulate a major source of your garage’s heat: the garage door. However, rigid foam insulation sheets aren’t cheap—unless you get creative.
Hack the foam market
The foam boards sold at cheaper retailers like Dollar Tree aren’t technically meant for home insulation. They’re usually bought for arts and crafts. However, inside the outer layers of kraft paper is a polystyrene foam core—an excellent insulator. The air pockets in the foam trap heat, preventing it from entering your garage.
The sheets, sized 20 inches by 30 inches, are available for $1.25 each online or in-store at your local Dollar Tree. Some stores reportedly offer a 25-pack for $20, which doesn’t save money but is more convenient and reduces packaging waste. Each sheet covers exactly 4.17 square feet, so measure your garage door beforehand to calculate how many sheets you need. Typically, single garage doors are 8 or 9 feet wide by 7 feet tall, while two-car garages often have one large door, usually 16 feet wide by 7 feet high.
For comparison, a purpose-made garage door insulation kit from Home Depot costs $52.18 for a single-width door as of June 2025 and covers 60 square feet. Dividing $52.18 by 60 square feet gives a per-square-foot cost of $0.87 for the Home Depot option versus just $0.30 per square foot for the DIY Dollar Store solution. While there are clever ways to save money at Home Depot, this isn’t one of them.
Simply cut and paste, or, tape
To install your budget-friendly garage door insulation, you’ll need a few tools and supplies. Start with a ladder or step stool to reach the upper sections, a utility knife, and ideally a straightedge to cut the foam sheets cleanly. If you don’t have a dedicated straightedge, a ruler or scrap of lumber will suffice. Use a tape measure to determine the size of each garage door section between its horizontal beams.
Note that some garage doors have a pattern of many individual “squares,” while others have four or five long panels. The amount of bracing inside the door where you’ll insulate varies by design and region. For instance, garage doors in hurricane-prone Florida, with its expensive home insurance, have extra metal bracing to withstand high winds. You’ll need to work around such framework when cutting your foam sheets to size.
Once you’ve found a system to snugly fit the foam boards, secure them with duct tape or a similar adhesive to the inside of the door, sealing any seams. Ambitious types can use a double layer of foam boards for extra insulation. Fortunately, this method is affordable enough that even with a second layer, the cost will remain lower than purpose-made products.
