Radiant Barrier vs Insulation For Your Garage: Which is Better?

Radiant Barrier vs Insulation For Your Garage: Which is Better?

I’ve been talking about the benefits of insulating your garage for a while. But deciding what type of insulation you need can be a challenge.

Usually it comes down to a choice between a radiant barrier, or some type of fiberglass or foam insulation.

Depending on where you live, your garage probably gets either really hot in the summer, or really cold in the winter.

Radiant barriers and standard insulation are very different, but they help regulate temperature and humidity levels in your home.

Deciding which is best depends heavily on what region of the country you live in, as well as other factors. However, the best solution will usually be a combination of both. That helps to make your garage (and home) cozier, without breaking your wallet.

Keep reading to learn more about the differences between radiant barrier and insulation, and which is best for your home. To get a better understanding, we first need to learn how heat flows. 

The Three Ways That Heat Flows

Understanding the three ways that heat can move will help you understand how radiant barriers and standard insulation works for your home.

Remember that heat always travels from high-temperature zones to those with lower ones. In winter, heat will try to escape from your home through the roof, walls, windows, and floors. In summer, that heat will use those same areas to try to warm up the cooler air indoors.


Heat transfer by convection involves the physical movement of liquids and gases.

It occurs when there is a temperature difference between two parts of a liquid or gas. This causes the hot part to rise and the cooler one to sink. This is because colder materials have more density than hotter ones. 

If you’ve seen steam rising from a hot cup of coffee, you’ve seen convection at work. Another example is when frozen food thaws quickly under cold running water.


Conduction is caused by physical contact, with heat transferring from one material to the other.

If you wrap your cold hands around that cup of coffee we mentioned earlier, the heat will travel from the coffee, through the mug and then to your hands.

Standard insulation specializes in blocking conductive heat transfer by slowing it down as it goes through your walls. Materials like metal and concrete are great conductors of heat, while wood and insulating material are bad ones.


The final method of heat transfer is by radiation. We’re not talking about the kind of radiation that’ll make you glow, however.

Electromagnetic radiation, like microwaves and visible light, causes radiant heat to travel through space. There is no direct contact between the heat source and material.

We’ll stick with the coffee example one last time. If you put the cup in the microwave, the electromagnetic radiation isn’t heating up the air in the microwave. That’s why there’s not a blast of hot air when you open the microwave door.

Instead, the radiation directly heats up the cup of coffee itself.

Radiation from the sun is the main reason why your home collects so much heat in the summer. Radiant barriers can help prevent it from entering your home. 

Radiant Barrier

Unlike standard insulation, radiant barriers work by reflecting radiant heat away from your house.

It works by using a highly reflective film attached to one side of a base layer of plastic, cardboard, kraft paper, or oriented strand board. Sometimes, fiber is used to reinforce radiant barriers, making them easier to handle and more durable. 

The reflective material reflects the solar radiant heat instead of absorbing it. That slows conductive and convective heat flow.

However, that reflective ability only works when the reflective surface is facing an open air space. The air gaps help keep the foil ventilated, while lowering the temperature and keeping the air dry. 

There should be a gap of between ½ and ¾ inches for radiant barriers. This is true even if they are installed in a wall or under a roof. There still needs to be some sort of air gap. 

Even though radiant barriers are associated with blocking the summer heat, they can also prevent your garage from losing heat in the winter.

By facing the reflective part of the radiant barrier inside, it can reflect heat back into the garage. 

In the right environment, radiant barriers can help lower energy costs by between 5% to 10%. They are not designed to reduce heat conduction as effectively as standard insulation. 


Emissivity represents the amount of radiant heat that materials emit instead of reflecting.

The best radiant barriers will have low emissivity levels represented as a number between zero and one, or a percentage. The manufacturer fact sheet or the product label should indicate that information.

For example, a radiant barrier with emissivity levels of 0.03 to 0.05 will have a reflectivity that ranges between 95% to 97%. 

Radiant barrier in a roll

How to Install a Radiant Barrier

Before installing a radiant barrier, it’s important to learn about your local building and fire codes and read the manufacturer’s instructions, and safety precautions.

The Reflective Insulation Manufacturer’s Association International provides installation tips and more information.

It’s easier to install radiant barriers in new buildings. However, you can also add them to existing construction with a little extra work.

Before you begin, you’ll have to decide whether you want to keep your garage warm or cool.

As we talked about earlier, reflective foils placed facing outside will keep your garage cool. Having them facing the inside will maintain its warmth.

Remember that you will also have to leave or create air gaps for the radiant heat to flow.

Since reflective foil conducts electricity, be careful not to touch any bare electrical wiring while adding radiant barriers. 

Common Problems with Radiant Barriers

There are some common problems with radiant barriers that prevent them from working correctly.

If dust accumulates on the reflective surface, it can reduce it’s efficiency. The reflective surface should remain as clean and shiny as possible.

A dirty or dusty radiant barrier will trap the heat, not allowing it to reflect away from your home. This, in turn, allows the heat to penetrate your garage roof and walls, heating it up.  

Cold climates have the additional risk of developing condensation and collecting moisture on the underside of the radiant barrier foil.

Not only will this prevent your radiant barrier from working efficiently, but it can cause mold or even water damage. You can avoid moisture issues by using perforated radiant barriers or inspecting the ceiling regularly for leaks. 

Finally, a common myth is to place a radiant barrier directly on the underside of a roof. However, without proper an air gap for ventilation, your roof temperature will still increase significantly.


Now let’s talk about how standard insulation can work for your garage.

It’s easy to think of insulation as a thick blanket that wraps around your garage. It helps keep the heat inside while also reducing energy usage from heaters.

Not only does standard insulation keep your house warmer during winter, but also help block heat from getting in during the summer. 

Unlike radiant barriers, standard insulation is efficient at slowing down the conductive heat that flows through your walls. It also reduces convective heat to a lesser degree.

Also, standard insulation doesn’t need an air gap like radiant barriers. It deals with conductive heat and requires physical contact. 

People use heating systems to replace heat that escapes to colder areas during the winter. Proper insulation effectively slows down that heat flow as it travels toward lower temperatures.

How effective a particular insulation is at slowing down heat transfer is called it’s R-Value.


R-value is a measurement of how effective insulation is at blocking heat transfer. The higher the R-value, the more effective the insulation is.

However, R-values aren’t measured on a linear scale. Meaning that R-19 insulation is more effective than R-13 insulation, yes.

However, it’s more like a 5% improvement, rather than a 45% improvement.

The type of insulation, density, thickness determines the R-value of different insulating materials. You can also increase the R-value by adding more layers of insulation, or by making it thicker.

The recommended R-value amount varies for different locations. It depends on your climate zone, the part of the house, and your HVAC system.

Finally, different types of insulation resist heat flow differently.

The most common type of insulation is batt insulation, usually made from fiberglass or mineral wool. You can also get foam insulation in either panels, or spray-foam insulation. You can find out the differences between spray foam and batt insulation in my article here.

Each insulation type has slightly different R-values, and is optimized for different parts of your house, or different applications. However, in general, an insulation with a higher R-value resists heat transfer better than one with a lower R-value.

Fiberglass vs. Mineral Fool Insulation

Fiberglass insulation is made up of tiny glass fibers, reinforced by plastic, making it strong and very efficient. It can be cut to fit, and installed on floors, ceilings, and walls and is fitted between studs, joists, and beams. 

It’s one of the most popular options for insulation because it’s relatively cheap, easy to install, resists fire.

Unfortunately, they can trap moisture and dust that promotes mold growth. Its particles can also cause rashes and irritation on people’s skin, nosebleeds, and respiratory failure if inhaled. 

Mineral wool insulation, also known as stone or rock wool, may look like fiberglass insulation but is actually thicker and denser. That helps it reduce noises from both outside and inside of the garage, like when the garage door opens.

This is the type of insulation I use inside my garage walls to help regulate the temperature.

It’s comprised of non-metallic raw materials, and 70% of those materials are recycled. In general, mineral wool insulation has a slightly higher R-value and is more eco-friendly than fiberglass.

Mineral wool is also a non-combustible material and naturally resistant to moisture, allowing it to insulate even when wet.

However, it is more expensive than fiberglass. It’s heavier weight can make it challenging to fit in certain spots. It is also not available in a wide range of sizes like fiberglass. 

Can Insulation Cool Your Home During The Summer?

Contrary to popular belief, insulation doesn’t actually cool (or heat) your home.

However, by slowing down the transfer of heat, insulation will make it harder for the outside heat to warm up your garage.

For example, by insulating one wall of my garage, and the garage door, I’ve cut my daily maximum temperature by over ten degrees in the summer.

Slowing down the heat flow helps make your house feel cooler, without having to run the AC so much.

Radiant Barrier vs. Insulation: Things To Keep In Mind About Your Garage

Radiant barriers are ideal in hot climates, while standard insulation is more efficient during cold winters. Ideally, the best solution would incorporate both types.

This can also prevent plumbing issues and pipes from freezing in the garage and stop the spreading of mold and mildew.

You will also have to insulate your garage door in order to get the best out of your insulation system. However, make sure that your insulation materials won’t add excessive weight. That could potentially damage your garage door.


These are some common questions about radiant barriers and insulation.

Do I need insulation if I have a radiant barrier?

Standard insulation and radiant barriers can work independently from each other in different locations. Combining both will guarantee better indoor temperatures and lower energy bills.

Will a radiant barrier keep the heat in?

With the proper installation, radiant barriers can efficiently keep heat indoors while reflecting solar radiation away. 

Are radiant barriers worth the money?

Radiant barriers are definitely worth it if you live in a hot region, but are effective during every season. The US Department of Energy says that radiant barriers can minimize cooling costs by 5% to 10%. It also increases your property value by making it more energy-efficient.

Can radiant barriers cause mold?

Mold needs a couple of important things to grow, most notably moisture and darkness. With that in mind, radiant barriers don’t cause mold by themselves.

However, by their very nature, radiant barriers do limit the air-flow around them. If moisture gets in front of the reflective surface, with nowhere to go, then it could promote an environment where mold can grow.

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