A New Era of Insulation: What Is Aerogel Felt?

Aerogel felt is a soft, flexible sheet made by combining aerogel with strong fibers. Aerogel alone is usually a fragile and powdery material. But when blended with materials like polyester or glass fiber, it turns into a roll or mat that you can bend, cut, or layer. That helps engineers and builders use it more easily.

People use aerogel felt where other insulation materials do not work well. It performs better in very hot or cold spaces. It also fits into small or tight areas. Its biggest strength is very low thermal conductivity. That means it slows down the flow of heat better than most other materials. This special feature makes it very useful in buildings, ships, airplanes, and even space missions.

What’s Inside Aerogel? The Secret to Low Heat Flow

Aerogel looks like a solid. But inside, it’s mostly empty space. In fact, more than 90% of aerogel is just air. But the air is trapped in tiny pores, each smaller than a virus. These tiny holes stop gas molecules from moving freely. That means heat cannot travel easily through air inside the material.

The solid parts of aerogel are also special. They are thin, winding paths that twist around. This long path slows down how heat moves through the solid itself. Since there are fewer contact points, heat cannot pass through quickly.

Some types of aerogel also block heat from light. They scatter or absorb infrared rays before the heat gets far. So, heat has trouble moving through all three paths: gas, solid, and radiation. That’s why aerogel has one of the lowest thermal conductivities on Earth.

How Felt Structure Changes the Way Heat Moves

Unlike pure aerogel, aerogel felt has extra materials—mainly fibers. These fibers hold the aerogel in place and make the material strong and flexible. But they also affect how heat moves.

Different types of fibers have different results. Glass fibers are harder and conduct more heat. Polyester fibers are softer and conduct less. The more fiber you add, the stronger the material becomes. But more fiber can also give heat more paths to travel.

The felt's density also matters. When you press the material and increase its density, it has less air. That increases contact between solid parts, which speeds up heat flow. The same happens when the felt is compressed during use.

There are also different ways to combine aerogel and fiber. Some use coatings. Some fill the gaps between fibers. These changes shift the size and shape of pores. That can help or hurt how well the material blocks heat. So, the design of the felt changes its overall thermal performance.

How Do Scientists Measure Thermal Conductivity?

To know how well aerogel felt stops heat, scientists need to measure its thermal conductivity. They use special tools and methods to test how fast heat passes through the material. Each method has its strengths. Some are better for thick samples. Others are faster or more exact. Here are the most common and useful ones:

Heat Flow Meter Method (HFM)

This method is used often for building insulation and thick aerogel felts. It works in a very clear way. One side of the sample touches a hot plate. The other side touches a cold plate. The machine measures how much heat flows from one side to the other.

The sample must be flat and smooth. This helps the plates touch the surface evenly. The test usually runs until a steady temperature is reached. That means the heat flow does not change over time.

This method follows well-known standards like ASTM C518 and ISO 8301. It is good for samples that are 10 mm or thicker. Results are easy to repeat, but the setup must be done carefully. If the sample has air gaps or folds, results may not be correct.

Guarded Hot Plate Method (GHP)

This method gives very high accuracy. It also uses a hot plate and cold plate, but adds special guard heaters around the sides. These extra heaters keep heat from leaking out through the edges of the sample. That way, all the heat moves only in one direction—top to bottom.

The system controls temperature very tightly. The sample must be the exact right size and shape. The plates must press evenly on the material. It often takes hours to complete one test. But the results are trusted worldwide, especially in research labs. This method is often used to check or calibrate other testing tools.

Transient Hot Wire (THW) and Transient Plane Source (TPS) Methods

These are fast and flexible methods. Instead of plates, they use a heating wire or thin sensor placed inside or on the surface of the sample. The sensor heats up for a short time. A computer watches how the temperature around the sensor changes.

From this, the system calculates how fast heat moves through the material. These methods are helpful for soft, uneven, or powder-like samples. Aerogel felt is a good match because it may not always stay flat or dense.

THW is often used for loose aerogel powders or small test pieces. TPS is good for layered materials like aerogel felt. These tests follow standards such as ISO 22007-2.

These methods are quick—some finish in just a few minutes. They also need less sample preparation. But the results may vary if the sample is too thin or if the heat spreads unevenly.

Real-World Factors That Affect Heat Performance

In lab tests, aerogel felt often shows very low thermal conductivity. But outside the lab, many conditions can change how well it insulates. These real-world factors are important for engineers, builders, and designers who use aerogel felt in buildings, vehicles, pipelines, or space systems.

Temperature

As the temperature goes up, thermal conductivity also goes up. This is not a flaw—it is a physical rule. At high temperatures, heat moves more through radiation, especially in materials with large pores or thin walls. Silica aerogel can handle this better than many other materials, but above 300°C, the radiation part becomes stronger.

To reduce this effect, some aerogel felts include infrared opacifiers (like carbon black or titanium dioxide). These additives block or scatter infrared rays. That helps the material stay insulating even when the outside temperature gets very high.

Humidity

Aerogel has millions of tiny pores filled with air. But in wet air, water vapor can enter these pores. Water has a much higher thermal conductivity than air. So, even a small amount of moisture hurts the performance.

Long exposure to humidity may also cause the aerogel’s structure to weaken. The soft parts may start to clump, crack, or lose shape. Some products use hydrophobic treatments on the surface to stop water from getting in. But these coatings can wear off over time, especially under pressure or heat cycling.

Compression

Aerogel felt is soft and compressible. When it is pressed too hard—such as under clamps, screws, or weight—the air pockets shrink. This increases solid contact paths inside the material. Heat then flows faster.

Even small compression (10–20%) can raise the thermal conductivity. In tight installation spaces, engineers must calculate the compression level and use spacers or protective layers if needed. Some felt types are designed with compression recovery, meaning they return to normal shape after being released. But not all do.

Aging

With time, aerogel felt may not perform as well as when it was new. Reasons include:

• Dust or dirt filling the pores
• Moisture slowly getting in
• Structural settling under its own weight
• Repeated heating and cooling cycles

All of these can change the internal pore structure. The insulation quality may drop slowly over months or years. That is why aging tests under heat, moisture, and pressure are required for long-term projects, especially in aerospace, oil and gas, or energy storage.

Environmental Gases

Aerogel’s performance depends on the gas trapped inside its pores. Usually, this gas is air. But if the environment has helium, hydrogen, or other special gases, the thermal behavior changes.

For example, helium conducts heat five times faster than air. If helium fills the aerogel’s pores, heat moves more quickly. Engineers must consider this when using aerogel felt in sealed environments, like cryogenic tanks, aerospace cabins, or lab equipment.

Special designs may use gas barriers or layered structures to control gas exposure. Knowing the surrounding gas type is key to predicting how the aerogel felt will behave.

Answering Common Questions About Aerogel Felt