An airbag is made of a nylon fabric bag, a chemical propellant that generates nitrogen gas, a metal inflator housing, electronic crash sensors, and a fine filter to cool the gas before it reaches the bag. Each component uses specific materials chosen to survive years of dormancy inside a steering wheel or dashboard, then perform flawlessly in the roughly 30 milliseconds between a crash and full inflation.
The Fabric: Woven Nylon With a Silicone Coating
Nearly all airbags worldwide are made from woven nylon 6,6, a strong synthetic fabric where two sets of threads interlace at right angles. Other nylon types (nylon 6, nylon 4,6) and polyester appear in some designs, but nylon 6,6 dominates because of its combination of high tensile strength, heat tolerance, and ability to fold tightly for years without degrading.
Raw nylon alone can’t handle the job. The fabric gets a thin coating of silicone elastomer, which does two things: it controls how much gas can seep through the weave (too permeable and the bag deflates too fast, too tight and it won’t cushion properly), and it protects the nylon from the intense heat of the inflation gas, which can reach several hundred degrees. Early airbags used neoprene coatings instead of silicone, but silicone offered more flexibility in tuning gas permeability and better long-term stability.
If you’ve ever seen the white powder that puffs out when an airbag deploys, that’s cornstarch or talcum powder. It’s packed into the folded bag as a lubricant so the fabric doesn’t stick to itself during storage. Without it, the layers could bond together over years and slow deployment. People often mistake this powder for smoke in the seconds after a crash.
The Propellant: From Sodium Azide to Safer Alternatives
The gas that fills an airbag is mostly nitrogen, and it comes from a controlled chemical reaction, not a compressed gas canister. For decades, the standard propellant was sodium azide, a white crystalline compound that decomposes rapidly into sodium metal and nitrogen gas when heated. Sodium azide was effective because it produced pure nitrogen within a fraction of a second, but it’s also highly toxic. Even after the reaction, incomplete combustion could leave azide residues that posed respiratory, skin, and eye hazards to crash survivors and first responders.
Most manufacturers have moved away from sodium azide. The leading replacement combines guanidine nitrate as the fuel and basic copper nitrate as the oxidizer. Guanidine nitrate is about 49% nitrogen by mass, making it an efficient gas source. It ignites at relatively low temperatures, costs less than many alternatives, and produces far less toxic byproducts. This combination has become the industry benchmark against which newer propellants are compared.
Other non-azide alternatives have been explored, including nitrogen-rich compounds called azoles, pyrazines, and even aluminum-copper oxide nanothermites paired with copper complexes that generate a mix of nitrogen, oxygen, and nitrous oxide gases. The core goal is always the same: produce a large volume of cool, non-toxic gas as quickly as possible.
The Initiator: A Tiny Explosive Trigger
The propellant doesn’t ignite on its own. A small device called an initiator, or squib, provides the spark. When the crash sensor sends an electrical signal, the initiator fires using a pyrotechnic mix, traditionally zirconium potassium perchlorate. This compound ignites reliably from an electrical impulse and produces enough heat and pressure to set off the main propellant charge. Some newer designs use titanium subhydride potassium perchlorate instead, which generates more gas during ignition and is less sensitive to accidental static discharge.
The Inflator Housing: Sealed Steel
All these chemicals sit inside a metal canister called the inflator, typically made from stamped stainless steel. Some designs use aluminum or copper components. The housing must stay perfectly sealed for the 10 to 15 year lifespan of the airbag, protecting the propellant from moisture and temperature swings. Thin metal seals, made from copper, aluminum, or stainless steel, plug the openings in the housing. These seals are engineered to rupture at a precise pressure when the propellant fires, acting as pressure-release vents that direct gas into the bag.
The tensile strength and thickness of the seal material determine exactly when it breaks open. If the seal is too strong, inflation is delayed. Too weak, and the propellant gases could leak over time or vent unevenly.
The Gas Filter: Stainless Steel Mesh
Between the propellant and the fabric bag sits a filter made from layers of flat, braided stainless steel mesh. These layers are stacked and compressed to create a dense metallic screen, typically with a bulk density of 3.0 to 5.0 grams per cubic centimeter. Common stainless steel grades used include SUS304, SUS310S, and SUS316.
The filter serves two purposes. It traps solid particles and residues from the chemical reaction so they don’t reach the bag or the occupant. It also cools the gas significantly, because the hot gas transfers heat to the metal mesh as it passes through. Some designs use a two-layer filter where the inner layer has coarser mesh and the outer layer has finer mesh, progressively filtering and cooling the gas before it enters the bag.
The Crash Sensor: Silicon Chips
The decision to fire the airbag comes from MEMS (micro-electro-mechanical systems) sensors, tiny devices built on silicon chips. Silicon has been the standard material for automotive sensors for over 20 years because it’s compatible with microprocessor manufacturing and can integrate multiple functions onto a single chip. These sensors detect rapid deceleration, and when the force exceeds a threshold, they send the electrical signal that fires the initiator. Modern vehicles use multiple sensors placed around the car to distinguish between a minor fender-bender and a collision severe enough to warrant deployment.
What Happens to the Materials After a Crash
After deployment, an airbag becomes waste, and recycling it has historically been difficult. The steel inflator housing is easy to recycle through standard metal recovery. The nylon fabric is the challenge: that silicone coating bonds tightly to the nylon, and separating the two without destroying the fabric requires specialized chemistry.
Recent research has developed a method using potassium hydroxide as a catalyst in isopropyl alcohol to break down the silicone coating through a process called siloxane bond exchange. This dissolves the silicone while preserving the nylon’s strength, and the solvent can be recovered and reused. The recovered nylon is clean enough to be repurposed as reinforcement fabric, interior automotive parts, or engineered textiles. This approach could make a meaningful dent in automotive polymer waste, since airbag fabric is otherwise difficult to separate from its composite layers and typically ends up in landfills.