Is Cardboard a Good Insulator? What You Need to Know

With rising energy costs, many people are looking for ways to better insulate their homes or packaging to keep things cold or hot. One material that often comes up in discussions around insulation is cardboard. Cardboard is readily available, inexpensive, and seemingly has some insulating properties. But is cardboard actually an effective insulator?

In this article, we’ll explore whether cardboard makes for good insulation compared to other common materials. We’ll look at the structure and properties of cardboard that determine its effectiveness as an insulator. We’ll also discuss the advantages and disadvantages of using cardboard for things like insulation in walls or flooring, keeping food and liquids hot or cold during transport, and other use cases. By the end, you’ll have a better understanding of how cardboard performs as an insulator so you can decide whether it is a good choice for your particular needs.

Contents

What is Cardboard?

Cardboard refers to heavy-duty paper material that is thicker and more durable than standard paper. The most common type of cardboard is corrugated cardboard, which consists of a fluted corrugated sheet sandwiched between two flat linerboards.

Corrugated cardboard is made by combining three layers:

The inner fluted layer is called the corrugating medium. It is made by passing paper through corrugated rollers which give it a wavy shape. This layer gives cardboard its bending strength.
On either side of the corrugated medium are the outer flat layers called liners. They are typically made from kraft paper or recycled cardboard. The liners provide a smooth surface and protect the medium from damage.
An adhesive (starch based or laminating) is used to bond the corrugated medium with the outer liners.

Standard cardboard has a high strength-to-weight ratio and is resistant to humidity, abrasion and crushing forces. It is lightweight but stiff and sturdy. These properties make corrugated cardboard ideal for packaging, shipping containers, displays, and other industrial uses. Cardboard can also refer more generally to heavy paper-based materials like folding boxboard used in folding cartons.

Types of cardboard

Type	Description	Common Uses
Corrugated cardboard	Consists of fluted corrugated medium between two flat liners.	Packaging, boxes, provides high bending strength.
Folding boxboard	Made from multiple layers of paper.	Folding cartons, packaging.
Cardstock	Thicker, more durable paper stock.	Business cards, postcards, covers, etc.
Paperboard	General term for thicker, stiffer paper material.	Various applications, can be single or multi-layered.
Chipboard	Paperboard made from recycled paper stock. Low density and cost.	Signs, boxes, sleeves.
Paper tube/Roll	Made by winding paper material into a tube shape.	Shipping, forms, yarn, etc.
Strawboard	Thick paperboard made from straw pulp.	Box partitions, displays.
Bristol board	Thin and smooth cardboard used for artists’ canvases, greeting cards, tags, etc.	Artistic and decorative applications.
Duplex board	Double-layered board with different materials on each side.	Product packaging.

The main distinction is between corrugated cardboard with its iconic corrugated fluting and paperboards which have a more solid layered structure. But in general, cardboard covers a wide range of heavy paper-based materials with varied properties and applications.

Why is Cardboard a Good Insulator?

Cardboard is primarily composed of cellulose fibers derived from wood pulp or recycled paper materials. Cellulose is a structural polysaccharide made up of long chains of glucose monomer units bonded together.

The cellulose chains are held together by strong hydrogen bonds. These hydrogen bonds allow cellulose to form linear microfibrils which give cardboard its strength and stiffness. The cellulose fibers are also hydrophillic, meaning they attract and absorb moisture.

In addition to cellulose, cardboard contains:

Hemicellulose – Branched polysaccharide polymers that strengthen the structure.
Lignin – Polymeric organic substance that makes the fibers rigid and water-resistant.
Binders – Adhesives like starch or laminates that hold fibers together.
Fillers – Materials like china clay to improve texture.
Sizing – Substances to improve moisture resistance.

How cardboard traps air and prevents heat transfer

Cardboard is able to resist heat transfer and insulate effectively because of its honeycomb-like structure which traps thousands of tiny air pockets.

Specifically, the corrugated layer in cardboard contains flutes or ridges. These flutes create air cavities that run through the entire thickness of the cardboard. The air pockets within the corrugations prevent direct contact between the cardboards’ top and bottom layers.

This separation created by the inner layer of trapped air pockets provides thermal resistance or insulating properties. Air is actually a very poor conductor of heat. The tiny air pockets significantly slow down the transfer of heat through the cardboard via conduction.

The up-and-down shape of the flutes increases the length of the pathway that heat would need to travel from one side of the cardboard to the other. This circuitous route inhibits conductive heat flow.

The air pockets also reduce heat loss through convection as the air has little room to circulate. And the closed cellular structure minimizes heat transfer by radiation.

The numerous air voids in cardboard physically block and resist the main methods of heat transfer – conduction, convection and radiation. This “blanket” of trapped air is what gives cardboard its effectiveness as a versatile insulator.

Comparison of cardboard’s conductivity to other insulating materials

This table provides a comparison of cardboard’s thermal conductivity to other common insulating materials in terms of their thermal conductivity values (measured in watts per meter-kelvin, W/mK).

Insulating Material	Thermal Conductivity (W/mK)
Cardboard	0.06
Fiberglass	0.04
Mineral wool	0.04
Cellulose	0.04
Polystyrene	0.03
Polyurethane foam	0.02
Aerogel	0.02

Thermal conductivity measures how well a material conducts heat. Lower numbers indicate better insulating capability.

As you can see, cardboard’s thermal conductivity rating of 0.06 W/mK makes it a decent insulator, though not as effective as plastic or foam alternatives. Materials like fiberglass, mineral wool, cellulose and polystyrene foam have about 50% better insulating capacity than cardboard – mostly in the 0.03-0.04 W/mK range.

The very best industrial insulators, such as aerogel and polyurethane foam, are around 3 times more effective at slowing heat transfer than cardboard. They have extremely low conductivity values of 0.02 W/mK.

While cardboard can insulate fairly well, its thermal conductivity is higher than specialized insulation materials. But for basic applications, cardboard performs better than no insulation at all. Its widespread availability also makes it convenient for small insulating jobs.

Advantages of Using Cardboard as an Insulator

While cardboard may not offer the best insulating capabilities compared to materials like foam and fiberglass, it comes with a number of unique advantages that make it an appealing option for certain applications.

Cost-effectiveness

One of the biggest perks of using cardboard as insulation is its inexpensiveness compared to other insulators. Industrial insulation materials can be quite costly to purchase and install. Cardboard offers a much cheaper alternative:

Cardboard itself is inexpensive due to its paper-based composition and abundance.
It is lightweight and easy to transport.
Installation is simple and does not require hiring specialty contractors.
No additional finishes or treatments are required for plain cardboard insulating panels.

For small-scale projects or temporary insulation needs, cardboard can provide substantial cost savings over using more complex insulation products.

Availability

Another major advantage of cardboard is how readily available and easy to acquire it is:

Many households tend to have a steady supply of cardboard from online shipping boxes, product packaging, and other sources. This cardboard would normally be discarded but can be repurposed for insulation projects.
Cardboard can be sourced for free from various commercial and industrial facilities that deal with high volumes of cardboard waste.
Most retail outlets that sell household goods will carry basic cardboard sheets and panels. This makes pickup convenient.
For large scale projects, cardboard insulation can be custom manufactured and is easy to procure.

The widespread availability and abundance of cardboard as a material gives it a distinct advantage in accessibility for both small-scale and industrial applications.

Ease of Use and Installation

Unlike more complex insulation products, installing cardboard is extremely simple and straightforward:

Cardboard can be used in sheet form or cut into custom shapes or panels using only basic tools. No advanced cutting or manufacturing equipment is required.
It is light and can be quickly affixed to surfaces with adhesives or simple fasteners like staples.
No protective equipment like respirators or safety gear is necessary to handle cardboard during installation.
Cardboard is user-friendly for DIY projects – no previous expertise is required.
It can provide insulation for unusual or hard-to-insulate spots that would be difficult to service with other insulators.

The simplicity and flexibility of installation are major benefits that make cardboard so useful for one-off or experimental insulation applications.

Environmental Benefits

Lastly, cardboard provides some advantages from an environmental sustainability perspective:

Repurposing cardboard that would otherwise be discarded reduces waste.
Most cardboard is highly recyclable and biodegradable.
Cardboard insulation contains no toxic materials and produces no harmful VOC emissions.
Manufacturing cardboard is generally more eco-friendly than producing common insulators which use plastics.
Transportation environmental impact is low due to cardboard’s light weight.

For green building methods or sustainability-focused projects, cardboard insulation can align well with environmentally-conscious goals.

In summary, despite mediocre insulating qualities, cardboard remains a great go-to choice for affordable, available, and easy-to-use insulation in the appropriate circumstances.

Disadvantages of Using Cardboard as an Insulator

Cardboard is a versatile material with a wide range of uses, from packaging to craft projects. However, when it comes to insulation, cardboard has several significant disadvantages that make it less suitable compared to specialized insulation materials. In this article, we will explore these disadvantages in detail.

1. Vulnerability to Moisture and Humidity

One of the most significant drawbacks of using cardboard as an insulator is its vulnerability to moisture and humidity. Cardboard is primarily composed of paper fibers, which readily absorb water. When exposed to moisture, cardboard loses its structural integrity and insulating properties.

Moisture infiltration can lead to several problems:

Reduced Insulation Effectiveness: Wet cardboard becomes a conductor of heat rather than an insulator, allowing heat to pass through it easily. This defeats the primary purpose of insulation.
Mold and Mildew Growth: Moist cardboard provides an ideal environment for mold and mildew to thrive. This not only further degrades the cardboard but also poses health risks to occupants.
Structural Damage: Over time, moisture can weaken and disintegrate the cardboard, potentially causing structural damage to the building.

2. Flammability

Cardboard is highly flammable, and this poses a significant fire hazard. In the event of a fire, cardboard insulation can ignite quickly and contribute to the spread of flames. This is a serious safety concern, as it can lead to a more extensive and dangerous fire.

For buildings and structures that require fire-resistant insulation, cardboard is not a suitable choice. Fire-resistant insulation materials, such as fiberglass or mineral wool, are designed to withstand high temperatures and inhibit the spread of fire.

3. Limited Durability

Cardboard has a relatively short lifespan compared to other insulation materials. It can easily deteriorate over time due to factors like moisture, pests, and general wear and tear. This limited durability means that insulation made from cardboard may need to be replaced more frequently, increasing maintenance costs in the long run.

In contrast, many traditional insulation materials, such as fiberglass and foam board, are designed to have a much longer lifespan and can withstand environmental factors better.

4. Limited Thermal Resistance

While cardboard may provide some degree of thermal resistance, it falls short when compared to materials specifically engineered for insulation purposes. The thermal resistance of cardboard is relatively low, meaning it has limited effectiveness in preventing the transfer of heat between the interior and exterior of a building.

For effective insulation, especially in regions with extreme temperatures, it is essential to use materials with higher thermal resistance values, such as fiberglass, foam board, or cellulose insulation.

While cardboard has its merits in various applications, it is not an ideal choice for insulation in buildings or structures. Its vulnerability to moisture, flammability, limited durability, and modest thermal resistance make it less effective and potentially risky when used for insulation purposes. To ensure proper insulation and safety, it is advisable to opt for specialized insulation materials designed to meet the specific requirements of the project while adhering to safety standards.

Alternatives to Cardboard as an Insulator

When it comes to insulating buildings or structures, cardboard may not always be the most effective choice. There are various alternative insulating materials available, each with its unique advantages and disadvantages. In this article, we will provide an overview of some common alternatives to cardboard as an insulator and compare their pros and cons.

Overview of Other Insulating Materials

Insulating Material	Advantages	Disadvantages
Fiberglass Insulation	Excellent thermal resistance Resistant to moisture when properly installed Fire-resistant versions available Long lifespan	Can irritate skin and respiratory system during installation Must be handled carefully to prevent skin contact
Mineral Wool Insulation	Good thermal resistance Excellent fire resistance Resistant to moisture Sound-absorbing properties	Can be heavier than other insulation materials May require specialized tools for cutting
Cellulose Insulation	Made from recycled paper and wood products Good thermal resistance Excellent soundproofing properties Treated to resist pests and fire	Susceptible to moisture if not properly installed Requires professional installation for optimal performance
Polystyrene Insulation (EPS and XPS)	High thermal resistance Resistant to moisture Lightweight and easy to handle Available in various forms, including boards and rigid foam	Not environmentally friendly due to petroleum-based production Vulnerable to UV radiation and should be covered when used outdoors
Polyurethane Foam Insulation	Exceptional thermal resistance Provides an effective air barrier Can be used in various applications, including spray foam Resistant to moisture when properly installed	Requires professional installation May release volatile organic compounds (VOCs) during curing
Aerogel Insulation	Exceptional thermal resistance Lightweight and highly efficient Resistant to moisture Thin profile allows for space-saving insulation	Expensive compared to other insulation materials Fragile and can crumble if not handled carefully

Choosing the right insulation material depends on various factors, including your specific needs, budget, and environmental concerns. Each material has its strengths and weaknesses, so it’s essential to weigh these factors carefully before making a decision. Consulting with insulation professionals can also help you make an informed choice that best suits your project.

Conclusion

In this article, we’ve explored the use of cardboard as an insulator, delving into its properties, advantages, and disadvantages. As we conclude, let’s recap the key takeaways, provide recommendations for using cardboard as an insulator, and share some final thoughts and advice.

Recap of the Properties of Cardboard as an Insulator

Cardboard, a common and readily available material, offers some insulation properties, including its ability to slow down the transfer of heat. It can be a cost-effective choice for specific applications, such as temporary insulation or craft projects. However, cardboard also has notable limitations:

Vulnerability to Moisture: Cardboard’s propensity to absorb moisture makes it unsuitable for areas prone to dampness or high humidity levels.
Flammability: Cardboard is highly flammable, presenting a fire hazard in certain applications, especially where fire-resistant materials are essential.
Limited Durability: Compared to specialized insulation materials, cardboard has a relatively short lifespan and may require frequent replacement.
Limited Thermal Resistance: While it provides some thermal resistance, cardboard falls short of the effectiveness offered by purpose-designed insulation materials.

Recommendations for Using Cardboard as an Insulator

If you choose to use cardboard as an insulator for specific projects or applications, consider the following recommendations:

Moisture Mitigation: Ensure that the cardboard remains dry by applying moisture-resistant coatings or barriers when appropriate.
Fire Safety: Exercise caution when using cardboard as an insulator in situations where fire risk is a concern. Explore fire-resistant coatings or consider alternative materials for these scenarios.
Regular Maintenance: Be prepared for periodic replacement or maintenance, as cardboard may deteriorate over time.
Supplementary Insulation: In situations where cardboard’s insulation properties may be limited, consider combining it with other insulation materials for enhanced performance.

Final Thoughts and Advice

While cardboard can serve as a makeshift insulator for certain short-term or low-risk projects, it’s essential to recognize its limitations and potential drawbacks, particularly in critical applications like home insulation. For long-lasting, effective insulation, it’s advisable to opt for purpose-designed materials such as fiberglass, mineral wool, cellulose, or foam board insulation.

Ultimately, the choice of insulation material should align with your specific needs, budget, and safety requirements. Whether you’re working on a DIY project or a professional construction endeavor, selecting the right insulation material is crucial to achieving optimal thermal efficiency and ensuring the safety and comfort of the occupants.