How Is Aerogel Made? The Science of the Manufacturing Process

Aerogel is made by forming a wet gel from a chemical solution, then carefully removing the liquid from that gel so its delicate internal scaffold of nanoscale pores stays intact rather than collapsing. That second part, the drying, is the hardest and most expensive step, and it is the reason aerogel took decades to move from laboratory curiosity to commercial product. The process sounds simple in outline, but every stage involves tradeoffs between cost, speed, and the quality of the final material.

Building the Gel

The journey starts with a liquid solution, usually containing a silicon-based precursor like tetraethyl orthosilicate (TEOS) or sodium silicate dissolved in a solvent, often alcohol or water. A catalyst, either an acid or a base, triggers chemical reactions that cause tiny solid particles to form in the liquid. Those particles link together into longer and longer chains, eventually connecting into a continuous three-dimensional network that spans the entire volume of the liquid. At that point, the mixture stops flowing and becomes a gel, a solid skeleton saturated with the leftover solvent, much like a water-logged sponge.

The character of the final aerogel depends heavily on what happens during this gelation stage. An acid catalyst tends to produce a finer, more thread-like network, while a base catalyst creates a chunkier, bead-like structure with larger pores. Researchers tune the ratio of precursor to solvent, the type and concentration of catalyst, and the pH to control pore size, density, and transparency. A gel destined for a window insulation panel, for example, needs different internal architecture than one intended for a thermal blanket on a spacecraft.

Aging and Strengthening the Wet Gel

A freshly formed gel is fragile. Its internal skeleton is thin and full of weak spots where chains barely touch. If you tried to dry it immediately, it would almost certainly crack or crumble. So the gel sits in its mother liquor, or sometimes in a fresh solvent bath, for a period of hours to days in a step called aging. During aging, additional chemical bonds form at the junctions between strands, thickening and reinforcing the network. The compression strength of the gel increases with both the time and the temperature of aging, and using a more polar solvent tends to promote the cross-linking reactions that strengthen the structure.¹

Aging is not glamorous, but skipping it or cutting it short is a reliable way to produce a mediocre aerogel. The step is essentially giving the gel time to finish building itself at the molecular level.

Solvent Exchange

After aging, the gel’s pores are filled with whatever liquid was used during gelation, often water or an alcohol-water mixture. Most drying methods do not work well with water in the pores because water has high surface tension and can destroy the delicate structure during evaporation. The gel therefore goes through one or more rounds of solvent exchange, where the original pore liquid is gradually replaced with a solvent more compatible with the chosen drying method. For supercritical drying with carbon dioxide, the target is usually pure ethanol or acetone, since CO₂ mixes well with those solvents but not with water.

Solvent exchange is often the longest step in the entire production sequence. It relies on diffusion: the new solvent slowly soaks in from the outside while the old one migrates out. For a large or thick gel piece, this can take many hours or even days of repeated soaking in fresh solvent baths. Recent work has explored speeding this up by performing the exchange at elevated pressures and mild temperatures, a technique that has been shown to cut processing time by roughly 86 percent compared to conventional methods.²

Supercritical Drying

This is the step that defines traditional aerogel manufacturing and the one that makes it expensive. The core problem with drying a gel is surface tension. When a liquid evaporates from a tiny pore, the retreating liquid surface pulls on the pore walls with enormous force, enough to collapse the structure entirely. Supercritical drying sidesteps this by never letting a liquid-gas boundary form at all.

In the most common version, the solvent-exchanged gel is placed in a high-pressure vessel and flooded with liquid carbon dioxide. The CO₂ gradually replaces the ethanol in the pores. Once the swap is complete, the vessel is heated and pressurized past carbon dioxide’s critical point, around 31 °C and 74 bar. At that point, the CO₂ in the pores is no longer a distinct liquid or gas; it is a supercritical fluid with no surface tension. The pressure is then slowly released, and the fluid simply diffuses out of the pores without pulling on anything. What remains is the dry solid skeleton, now surrounded by air instead of solvent, with its original pore structure almost perfectly preserved.³

The result is a material that is typically more than 90 percent air by volume, with pores on the order of tens of nanometers across. Those tiny pores are what give aerogel its famously low thermal conductivity: the pores are smaller than the mean free path of air molecules at ambient conditions, meaning the trapped air conducts heat far less efficiently than ordinary still air. As aerogel density increases and the pores shrink further, this suppression of gas-phase heat conduction becomes even more pronounced.⁴

Supercritical drying produces the highest-quality aerogels, but the high-pressure equipment is expensive, the process runs in batches, and each batch takes hours. These constraints are a major reason aerogel remains costly and have driven sustained interest in alternatives.⁵

Ambient Pressure Drying

The most commercially promising alternative to supercritical drying is ambient pressure drying, sometimes abbreviated APD. The idea is to let the gel dry in an ordinary oven or even at room temperature, avoiding the need for high-pressure vessels entirely. The catch: you have to protect the gel from the destructive capillary forces that normal evaporation creates.

The trick is chemical surface modification. Before drying, the gel is treated with a silylation agent, most commonly trimethylchlorosilane (TMCS), which replaces the hydroxyl groups on the internal surfaces with hydrophobic trimethylsilyl groups. This modification does two things. First, it makes the internal surfaces repel water, which prevents the gel from reabsorbing moisture later. Second, and more important for the drying step itself, it enables what researchers call the springback effect: as the gel shrinks during drying under capillary pressure, the modified surface chemistry allows the compressed network to spring back to nearly its original volume once the liquid is gone.⁶ Controlling this springback is essential for making APD aerogels with reproducible properties.⁷

APD aerogels are not quite as pristine as their supercritically dried counterparts. They tend to have slightly higher density and slightly less perfect pore structure. But they are dramatically cheaper to produce and much easier to scale, which is why most aerogel insulation blankets on the market today are made using ambient pressure methods. The economics come down to equipment: an oven versus a pressure vessel.

Freeze-Drying

A third drying route freezes the gel and then sublimes the ice directly from solid to vapor under vacuum, bypassing the problematic liquid phase entirely. This is the same basic technology used to make freeze-dried food and certain pharmaceutical products. In gel science, the resulting materials are sometimes called cryogels to distinguish them from supercritically dried aerogels, though the terms get used loosely.

Freeze-drying avoids capillary collapse, but it introduces a different structural issue. As the pore liquid freezes, ice crystals nucleate and grow, and the expanding crystals push the gel’s polymer chains aside. The result is a pore structure dominated by the geometry of the former ice crystals, which are typically on the order of hundreds of micrometers across, far larger than the nanoscale pores in a supercritically dried aerogel. One study found that each pore in a freeze-dried scaffold resulted from the growth of one to a few ice grains, with a final mean pore size of about 280 micrometers.⁸

Those larger pores mean freeze-dried gels are not as good at blocking heat conduction as nanoporous supercritically dried aerogels. But they can be perfectly adequate for applications like tissue engineering scaffolds, filtration media, and acoustic absorption, where the large interconnected pore network is actually an advantage.

Beyond Silica

Silica aerogels get most of the attention, but the gel-then-dry framework applies to a wide range of materials. Carbon aerogels, for instance, are made by first creating a gel from organic precursors like resorcinol and formaldehyde, drying it, and then pyrolyzing (heating without oxygen) the dried gel to convert the organic skeleton into pure carbon. The resulting material is electrically conductive and has been explored for supercapacitors, battery electrodes, and water purification.

Graphene aerogels take a different approach. A dispersion of graphene oxide sheets in water is heated under pressure in a sealed vessel, which reduces the sheets and causes them to self-assemble into a three-dimensional monolith held together by physical interactions and partial chemical bonding between overlapping sheets.⁹ These aerogels are extraordinarily light and have attracted attention for their mechanical resilience, electrical conductivity, and ability to absorb oils from water.

Bio-based aerogels represent a growing subfield driven by sustainability concerns. Researchers have made aerogels from cellulose, chitosan, alginate, starch, and other biopolymers, using much the same sol-gel-plus-drying workflow.¹⁰ These bio-based versions are lightweight, thermally insulating, and biodegradable, making them candidates for food packaging and biomedical applications where silica’s non-degradability is a drawback.¹¹

Making Aerogels Less Fragile

Classical silica aerogel is notoriously brittle. A block of it looks like solidified smoke and can shatter from a moderate impact. This fragility has been one of the biggest barriers to practical use, and a huge amount of research has gone into fixing it.

The strategies fall into a few categories. At the molecular level, researchers modify the precursor chemistry to build a more flexible backbone, for example by incorporating organic bridging groups between the silicon atoms. At the structural level, assembling aerogels from nanofibers rather than nanoparticles can create a network that bends instead of snapping. And at the composite level, embedding the aerogel in or around reinforcing fibers, whether glass, ceramic, or polymer, produces blankets and boards that are far more handleable than monolithic blocks.¹²

Most commercial aerogel insulation products today are fiber-reinforced composites rather than pure aerogel monoliths. The fibers add mechanical toughness and make the material easy to cut, wrap, and install, while the aerogel in the spaces between fibers provides the insulating performance. Some products also incorporate opacifiers, tiny particles that scatter infrared radiation, to reduce radiative heat transfer at high temperatures, extending the useful range of aerogel insulation into industrial settings.

3D Printing Aerogels

Traditional aerogel manufacturing produces panels, blankets, or granules. If you need a complex shape, you either mold the gel before drying or machine the dried aerogel, both of which waste material and limit design freedom. Additive manufacturing, specifically a technique called direct ink writing (DIW), is changing that.

In DIW, a gel precursor is formulated into an ink that behaves like a thick paste under normal conditions but flows smoothly when pushed through a print nozzle. The ink is extruded in programmed patterns, building up a three-dimensional structure layer by layer. After printing, the structure goes through the usual aging, solvent exchange, and drying steps.¹³ Researchers have demonstrated this with both silica-based inks and cellulose nanocrystal inks, producing aerogel objects with controlled 3D geometry and minimal structural shrinkage after freeze-drying.¹⁴

The ability to print aerogel structures opens up applications that would be impractical with conventional fabrication, such as custom-shaped thermal barriers for electronics or patient-specific biomedical implants with engineered porosity.

Why Scaling Up Is So Hard

The fundamental bottleneck for aerogel manufacturing at industrial scale is the drying step. Supercritical drying requires high-pressure autoclaves, and each batch takes hours of pressurization, solvent exchange, and depressurization. That limits throughput and makes the process energy-intensive.⁵ Even with ambient pressure drying, which avoids the pressure vessels, the solvent exchange and drying stages still take considerable time and involve flammable organic solvents.

Cost has been the persistent barrier to wider adoption. Aerogel insulation outperforms conventional foam and fiberglass by a wide margin per unit thickness, but it costs many times more. For building insulation, that premium is only justified in niche situations where space is at a severe premium, like retrofitting thin walls in historic buildings or insulating subsea pipelines. In aerospace and industrial settings where performance per weight matters more than material cost, aerogel has gained a stronger foothold.

Ongoing research is focused on reducing production time at every step. High-pressure solvent exchange, continuous-flow supercritical drying, and rapid ambient-pressure methods all aim to convert aerogel from a batch product into something closer to a continuously manufactured material. Some companies have achieved meaningful cost reductions, but aerogel is unlikely to become as cheap as commodity insulation anytime soon. The physics of removing liquid from a nanoporous structure without destroying it simply demands time and care.

Handling and Safety During Production

Aerogel production involves chemicals and conditions that demand careful management. The sol-gel step often uses alkoxide precursors that are flammable and moisture-sensitive, and the solvents used in exchange and drying (ethanol, acetone, methanol) are flammable as well. Supercritical CO₂ itself is not flammable, but the high pressures involved require robust safety engineering.

The dried aerogel also raises handling questions. Silica aerogel dust is extremely fine, and because the particles are nanoporous, they have enormous surface area that can draw moisture from skin on contact, causing dryness and irritation. Workers processing aerogel typically wear gloves and dust masks. Regulatory frameworks for aerogel handling are still catching up to the material’s expanding use, and efforts to compile safety guidelines for production, transport, and end-use have been motivated by the current lack of comprehensive data on long-term exposure risks.¹⁵

Silica aerogel is chemically similar to ordinary sand and glass, and bulk silica is generally considered non-toxic. But the nanoscale structure of aerogel particles makes direct comparisons with bulk silica tricky, and the precautionary approach in most production facilities is to treat the dust as a nuisance particulate at minimum. Bio-based aerogels made from cellulose or chitosan sidestep some of these concerns, since their base materials are biocompatible, though the solvents and crosslinkers used during manufacture still require care.