The Complete Guide to Cardboard Insulation

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Many homeowners are repurposing cardboard boxes and sheets to make insulators for their attic and walls. Many don’t know of its potential and want to use cardboard to insulate their homes. And many are not so sure about it! So, after doing some research I’ve compiled this complete guide on using cardboard for home insulation.

Insulation properties of cardboard

Cardboard being a poor thermal conductor makes for a good insulator, which gives us the opportunity to put its insulation properties to good use. Corrugated cardboard boxes are used in packaging and shipping because of its low cost, which makes it even more desirable to insulation your windows, or attic at a budget price. Moreover, cardboard boxes are abundantly available, so can be re-used for a few months, if not forever before dumping it out for recycling. You can also make do some corrugated cardboard structures to insulate your home or car.

Thermal properties of cardboard boxes

Thermal properties describe the rate at which the cardboard transfers heat. It turns out to be a good insulator because of the tunnel like the fluted structure of paper between two sheets of kraft paper. Cardboards are basically tightly packed fibers and its corrugated structure traps air in its little pockets. The R-value of the cardboard is somewhere between R-3 to R-4 per inch. It is typically because of the air pocket as air is not a good conductor of heat and takes time to acquire or release heat. So, in winter it can keep your room warm and in summer it will keep your room cool. We also have to have safe insulator which brings us to its igniting temperature; cardboards would ignite between 500 – 800 degree Fahrenheit.

Cardboard has a low thermal conductivity which also makes it good at slowing down heat transfer. This makes cardboard a versatile thermal insulator which can be used in various application. 

Normally the glass works as an insulator that keeps heat from transferring in a and out of the room; but if the glass is broken and need an immediate fix, then your stacked cardboard boxes could be a great solution. This is also the reason why you may have seen many car owners have fixed garbage bag on their broken window. Although it serves well as a thermal insulator, a garbage bag is thin and can be easily damaged. Sheets of corrugated cardboard would a much better option. As I said, it keeps the space cool in summer and warm in winter. Being a good insulator, it can also be used to trap heat inside an object. You may find being used to trap heat for a homemade solar oven.

Why is Cardboard a Good Thermal Insulator?

Corrugated cardboard boxes are inexpensive material used for packaging as well as protecting the item it is transporting. This makes sense as some material in the box could need heat insulators, which is why cardboard boxes make for a great option. It’s condensed wood fiber and fluted layer traps air making it a good insulator. Many would treat the cardboard box with weather coats or hydrophobic spray to prevent weather damage and make it waterproof.

A corrugated cardboard paper is made of a layer of fluted heavy paper, sandwiched between two thin kraft paper or liners. There is double and triple layer corrugated cardboard which is using in industrial packaging and displays. Its structure, prevents conduction of energy (heat and electricity) from one object to another, even with a significant temperature difference. Other insulators include wood, air, stone, fiberglass etc. The wood itself is a good insulator and cardboards are made from dense wood fibers which add up to its insulating properties including the air pockets. Double walls are a great insulator witch a versatile application in a number of electrical appliances such as coolers and refrigerators. It is a good insulator because it traps air in between the walls, thereby retaining the temperature; keep the space cool or warm in its original condition. Corrugated cardboard is also made up of two layers of paper with a semi-hollow fluting layer in between, thus proving insulation.

Double-wall and triple-wall corrugated cardboard boxes provide great insulation. You can even glue multiple layers of corrugated sheets to increase its insulation property. The thicker and heavier the cardboard, the better is its insulation.

How to Use Corrugated Cardboard to Insulate Windows?

Windows cause over 25% of the home’s energy loss. This is commonplace from where your house will lose its heat. You can insulate your windows using corrugated cardboard sheets or shutters, which you can make out of old packaging boxes. To increase its insulation properties you can add a layer of aluminum foil to it.

  1. Measure the window’s glass, excluding the frame to get the dimension which you will cut out of cardboard boxes to make shutters.
  2. Cut out two pieces of cardboard for each shutter which will be glued together for better insulation.
  3. Cover each side of the cardboard with an aluminum foil by taping it around the edges.
  4. Glue two cardboard pieces keeping the aluminum foil facing away into one thick cardboard shutter. Do the same for both shutters.
  5. The cardboard shutters to your windows using a tape on all sides. The aluminum foil will reflect heat the cardboard will insulate from cold. This will keep your room warm in winter and cool in summer.

How to Use Shredded Cardboard to Insulate Your Attic?

Insulating your attic and walls using corrugated cardboard is an efficient and cost-effective option than buying commercial insulation, where both types of insulator will give a relatively similar level of insulation. However, here we will be using shredded cardboard boxes which will act as a homemade cellulose insulation. This is not just about energy, it’s  about repurposing cardboard boxes which might have been dumped in the landfill. This  brings us to repurpose cardboard boxes with oil spills and food grease on it, which otherwise couldn’t have been recycled.

  1. Put on your mask and safety glasses as you will be grinding cardboard boxes, which will create a lot of dust. So, it’s advised to work in a well-ventilated space such as garage or even outdoors. It would also be a good idea to wear gloves and long-sleeved clothing.
  2. Remove any tape, staples, labels, stickers etc from the cardboard box and make sure it’s dry with no bug infestation. If it’s infested with the bug, let it sit under the sun for a few hours. This is where you can use your pizza boxes which otherwise would not be recycled.
  3. Cut the cardboard boxes into small pieces which will then be shredded by a hammermill. Collect the shredded cellulose pieces in a dry container.
  4. Mix aluminum sulfate ¼ weight of the shredded cellulose. Then mix half the amount of lime in the mixture. The aluminum sulfate will keep bugs away and lime will eliminate its rusting properties. To make the cellulose fireproof mix some borax powder.
  5. Now spread the insulation material manually in the attic and inside the walls. Make sure to keep the mix well stirred so that all the ingredients mix evenly.  

Using Corrugated Cardboard for Cellulose Insulation

Shred recycle paper is usually taken as Cellulose. You can purchase it from the store or make for yourself using cardboard boxes and sheets as cellulose. Here, we will discuss its other aspects.

The insulation is technically done using blower where you can load the cellulose into the hopper and blow through a hose. Try to do it on attic cavities, attic floors, etc.

For the wall cavity, the cellulose is blown into the cavities from the outside. Remove the siding and you will have to drill some holes through which you will blow in the cellulose. In the event, you aren’t removing the siding, you can do it from the inside of the house.

Since the cellulose is blown in under high pressure, there is little change of gaps or air pockets in the installation. However, you can use an infrared scanner to ensure all cavities have been filled.

Being a blown in insulation system, it does take some prep work. You have to wear safety gear and have to shred a lot of cardboard boxes; in fact, you can shred just about any type of paper.

How is Recycle Cardboard Insulation is Efficient?

  • Cardboard insulation is basically repurposing old boxes including the ones that you can’t be recycle.
  • It uses less energy than fiberglass and foam.
  • Using in the home for insulation, it prevents greenhouse gases.
  • It provides better soundproofing if you use in walls, floors or ceilings.
  • It can be done at home all by yourself without removing much of the wall covering.

Can You Insulate Garage Doors with Cardboard?

If your garage door is made of metal, it can turn your garage into an oven in summer and into a freezer in winter. If you want a budget way of insulating heat,  cardboard sheets may seem like a great option and will work, but it’s dangerous and inefficient.

Garage doors aren’t like attic where your insulator will stay put undisturbed, instead, it will be used regularly which will significantly reduce the life of homemade cardboard insulators. Being in contact with metal even a thick sheet of cardboard sheet will still radiate some heat into your garage. But then again, you have to adjust the door springs to make room for the extra cardboard sheets. Furthermore, there is a change of fire hazard as garage room is meant to work with fire and there will be some sparks during metal work which could ignite the paper. Then again, if some water gets through the cracks, it would turn the boards into a pulp or make it heavier.

So, what is a better insulator option for garage doors?

  • Reflective sheets should be the first option. You may also find a reflective sheet on a bubble sheet base and you can insulate the whole door in $50. However, with the reflective sheets on, you can sneak in a few stips of triple-wall corrugated cardboard behind the insulator to an airspace, which will significantly increase its heat insulation properties.
  • Rigid styrofoam should be next on the list. This is yet another great solution to prevent heat radiation. However, it could be a bit messy to work with. Here too you can add an extra layer of corrugated cardboard sheets to insulation effective.
  • Fiberglass batts are another great solution, which is easy to install and easy to take off. It will take a day and will cost you nearly $200. However, with fiberglass batts you wouldn’t need cardboard sheet installation, still, you can go for it.

Top Heat Leak Spots Where You can Insulate Using Cardboard Sheets

Heating bill can dig a hole in your pocket if you are not careful of your home insulation. Be careful while insulating your house. You might miss out few hot spots right in front of your eyes. Here we are going to point out those hotspots and how you can use cardboard to insulate your house.

  • Air leaks in doors and windows

    You may think it’s insignificant, but it will cost you a lot in the long run. Cut out some strips from your old cardboard box and tape or jack in those leaks. However, window insulation kits will cost you just over $20.

  • Heat through window glass

    You can also counter out your room’s heat by low temperatures at night. Here’s where you can make do cardboard curtains which are really good at keeping rooms heat within. If you don’t find long sheets of boards, you can cut out square pieces and tie them hanging down using wires or tynes.

  • Door drafts

    A major portion of your rooms heat would be leaking through the door drafts (the space under the closed doors). It gets worse in winter. You can use a lot of material to seal of the door drafts, or you could just fold a piece of thick cardboard and snug it under the door.

  • Chimney hole

    If you have a broken fireplace damper you should expect a 30 percent increase in your heating bills. Keep the fireplace flue seal tight. Orelse, it will lose a lot of heat through the chimney. You can plug the hole with corrugated cardboard or use a bubble wrap. However, you can use a chimney balloon which will cost you just under $50; however, remember to take the balloon out before lighting a fire.

  • Attic air leaks

    For most homes, a lot of heat escapes through the attic. You could install a profession attic insulator or you could just staple some cardboard sheet taped with aluminum foil. It’s cheap and can be done in a day.

  • Outlet draft

    Sure, it’s not that significant but on the long run and considering all the collective outlets, it could add up to a pretty hefty cost. You can use foam or double-walled corrugated cardboard cutouts to seal off these outlet draft.

  • Radiant Barriers

    Another great way to protect your house in summer is by simply radiating back sun’s light; for which you need a reflective surface. Although you can purchase reflective panels from the store, you can make one for yourself at home using pieces of cardboard and aluminum foil, both of which are inexpensive. Just cut out a piece of cardboard from stack boxes, tape up aluminum foil and you are done! The place is facing away near the glass door or skylight and you can save a ton of heat from getting in.

How Much Can You Save By Insulating Your House?

You will be saving nearly $1500 -$2000 each year on energy bills if you design your house properly and make it energy efficient. 

Designing an Energy-Efficient House

Apart from using home insulation system if you could only design your house to be energy-efficient you can reduce up to 60% of your energy bills.

  • Design your house so that it received more light and sunshine from the north. So, the roof overhang should also be longer in length. This way the windows will be in shades in summer but will allow sun’s heat to get in in winter when the sun’s angle is low.
  • Install window shutters, awnings or shades to keep sun rays away in summer.
  • Have a sloping glass as a skylight that faces north. It will allow enough natural light to the house to eliminate using artificial ones.
  • Natural materials such as timber and clay can keep your home cool in summer and warm in winter. If you use mud bricks you will not only be saving on expenditures but also get natural heat insulation.
  • Concrete floors are good at absorbing heat during the day and releasing it at night. Moreover, an un-carpeted floor will absorb more heat than a carpeted floor.
  • Heat is lost faster through glass than insulated walls. So, as a good practice, you could open the curtain at day and shut it at night.
  • Plant some deciduous creeper in the yard. In summer they will give you shade and after fall they will allow sunlight in the winter.
  • Avoid having a tin roof as it loses a lot of heat in winter and gets too hot in summer; instead, insulate the roof or paint it white or using aluminum foil taped cardboard sheets.


Cardboard itself may not be enough to give a good insulation to your house, but you can use it along with other material to increase its insulating properties. It is inexpensive for temporary application such as making a ceiling out of cardboard. You can just stretch some wires nailed down to the four corners and simply hand taped cardboard sheets to create a shade. When the summer is over, take it down to let sun’s heat into the house.

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