Aerogel

Aerogel emerged from a bet. In 1931, Samuel Stephens Kistler at the College of the Pacific in Stockton, California, wagered with fellow chemist Charles Learned over whether anyone could replace the liquid in jelly with gas without causing the solid structure to collapse. The conditions for answering this seemingly whimsical question had finally aligned: Kistler's 1922 master's thesis at Stanford had explored supercritical fluids and amino acid crystallization, pressure vessels were becoming commercially available, and gel chemistry was understood well enough to attempt the manipulation.

The challenge was fundamentally structural. When liquid evaporates from a gel, surface tension at the retreating liquid-air interface pulls the delicate solid framework inward, crushing it into a dense, shrunken residue. This is why dried-out jelly becomes hard and small rather than maintaining its original shape. Kistler's insight was to bypass liquid evaporation entirely by exploiting a peculiar state of matter. By first replacing the water in a gel with alcohol through diffusion, then heating the gel in an autoclave past alcohol's critical point—the temperature and pressure where the distinction between liquid and gas disappears—he could depressurize without ever forming a liquid surface. The supercritical fluid simply became gas, leaving the original gel structure intact but now filled with air instead of liquid.

The result was a material unlike anything previously created: 99.8% air by volume, yet solid enough to hold in your hand. It was 39 times more insulating than the best fiberglass insulation available and 1,000 times less dense than glass. Kistler called his creation 'aerogel'—literally 'air gel.' Others would nickname it 'frozen smoke' or 'solid smoke' for its translucent, ethereal appearance that seems to hover at the edge of visibility. When you hold aerogel, it feels almost like nothing; a block that should weigh pounds weighs grams, and it transmits pressure and temperature in uncanny ways.

Kistler spent four years at the University of Illinois (1931-1935) characterizing aerogel's remarkable properties, publishing studies on thermal conductivity and catalytic behavior of various oxide aerogels. In the early 1940s, he licensed production to Monsanto Corporation, which manufactured silica aerogel under the trade names 'Santocel,' 'Santocel-C,' and 'Santocel-Z' at a plant in Everett, Massachusetts. For decades, aerogel remained more scientific curiosity than commercial success—the supercritical drying process was expensive, slow, and required specialized pressure equipment that most manufacturers didn't possess.

The material found its true purpose in the extreme conditions of space exploration. NASA's Jet Propulsion Laboratory perfected aerogel production for the 1999 Stardust mission, which used panels of aerogel to 'soft catch' comet particles traveling at hypervelocity—speeds of six kilometers per second. The porous structure slowed particles gently over millimeters rather than destroying them on impact, allowing the first samples from a known comet to return to Earth in January 2006, landing in a Utah desert.

On Mars, aerogel protects the rovers Spirit, Opportunity, and Perseverance from temperature swings between -96°C at night and +40°C during the day. The material's extraordinary insulation keeps electronics operational within their -40°C to +40°C tolerance range while minimizing power consumption—critical when every watt must be accounted for on missions millions of kilometers from any power source.

Today, flexible aerogel blankets developed from NASA research insulate oil pipelines, protect firefighters, and improve building efficiency. The bet between two chemists in a California college in 1931 has cascaded across nearly a century of materials science, proving that even playful questions about jelly can reshape how we explore the cosmos and insulate our homes.