A spall liner is a layer of protective material mounted on the interior walls of an armored vehicle. Its job is to catch and contain metal fragments that break loose from the vehicle’s own armor when it’s struck by a projectile, blast, or mine. Even when armor successfully stops a round from penetrating, the impact can send sharp, high-velocity shards of metal flying into the crew compartment. The spall liner acts as a secondary safety net, trapping those fragments before they injure the people inside.
What “Spall” Actually Means
When a bullet, shell, or shaped-charge jet hits a steel or composite armor plate, the energy of the impact doesn’t just disappear. On the outside, the projectile may shatter or liquefy against the armor surface. On the inside, the shock wave can fracture the inner face of the armor and launch small pieces of metal inward at high speed. These secondary fragments are called spall. They behave like shrapnel inside a confined space, and without protection, they’re a serious threat to crews, passengers, equipment, and electronics.
Spall can also come from the projectile itself. Fragments of the bullet’s jacket or core that don’t fully penetrate may still push through cracks or seams and scatter inside the vehicle. The combined effect of armor-born and projectile-born fragments makes the interior of an armored vehicle far more dangerous than most people realize, even during a “successful” hit that the armor technically stopped.
How a Spall Liner Works
A spall liner catches fragments the same way a baseball glove catches a fastball: by absorbing kinetic energy over a flexible surface rather than bouncing it back. The liner is made of multiple layers of tough, tightly woven fabric. When a metal fragment hits these layers, it pushes into them, stretching and deforming the fibers. Each layer absorbs a portion of the fragment’s energy until the piece slows to a stop and gets trapped between the plies.
This is fundamentally different from the vehicle’s primary armor, which is designed to resist penetration from the outside. The spall liner isn’t trying to stop an incoming round. It only deals with the secondary debris that the armor itself creates or lets through. That distinction is important: the spall liner is a secondary protective system, not a replacement for armor.
Materials Used in Spall Liners
Most modern spall liners are built from textile-based composites. The most common material is aramid fabric, the same family of synthetic fibers used in body armor. Brand names like Twaron and Kevlar are typical choices. These fibers are extraordinarily strong for their weight, with high resistance to tearing and excellent energy absorption. Some designs also incorporate layers of glass fiber or carbon fiber to fine-tune the balance between weight, stiffness, and fragment-catching ability.
Researchers have been experimenting with ways to boost performance without adding bulk. One approach involves treating aramid fabrics with a shear-thickening fluid, a liquid that instantly stiffens on impact. These fluids typically use tiny silica particles (around 20 nanometers across) suspended in a polymer carrier. Under normal conditions the treated fabric stays flexible, but when a fragment strikes it, the fluid locks up and helps the fibers resist penetration more effectively. Silicon carbide particles can also be added to increase friction between individual yarns, making the weave harder to push apart.
How Spall Liners Are Mounted
Spall liner panels are designed to be removable. They’re typically attached to the vehicle’s inner hull using hook-and-loop fasteners (the same concept as Velcro). Hook strips or panels are bonded to the vehicle’s interior walls, and the outer cover of each liner panel carries the corresponding loop material. This lets maintenance crews pull a damaged panel off and replace it without tools or permanent modifications to the hull.
Internally, the liner itself is built in ply sets: groups of fabric layers sewn together and connected by tie layers that are slightly larger than the fabric plies. These tie layers help distribute force across a wider area during an impact. A sewn outer cover wraps the whole assembly, with a binding strip stitched around the edges for durability. The result is a self-contained, carpet-like panel that conforms to the shape of the vehicle’s interior and can be swapped out in the field.
Which Vehicles Use Them
Spall liners are standard equipment in most modern infantry fighting vehicles and armored personnel carriers. The Bradley Fighting Vehicle, Sweden’s CV90, Germany’s Puma, the Piranha family of wheeled armored vehicles, and South Korea’s Redback all incorporate spall liner systems. Main battle tanks like the M1 Abrams use similar internal protection, though the specific configurations vary depending on the armor type and threat profile.
The technology isn’t limited to tracked vehicles. Wheeled armored trucks and mine-resistant vehicles used in counterinsurgency operations also rely on spall liners, especially along the floor and lower hull where mine blasts generate the most interior fragmentation. In these vehicles, the liner serves double duty: catching metal spall and helping contain fragments from improvised explosive devices that strike the underside.
Spall Liners vs. Spall Coatings
The term “spall” also comes up in the context of steel body armor plates, where the problem is similar but the solution is different. When a bullet hits a steel rifle plate worn on the body, fragments spray outward along the plate’s surface and can strike the wearer’s arms, neck, or chin. To counter this, manufacturers apply thick polymer coatings to the plate’s face. These coatings are flexible enough to stretch and trap fragments against the steel rather than letting them ricochet.
Standard truck bed liner coatings, which some companies have tried to repurpose for this role, generally lack the elasticity to hold fragments effectively. Purpose-built encapsulation coatings are significantly more effective. But these body-armor coatings are a different product from a vehicle spall liner. Vehicle liners are multi-layered fabric panels designed to stop larger, faster fragments generated by anti-tank weapons and heavy munitions. The physics are the same, but the scale and engineering are in a different category entirely.
Why Weight Matters
Every kilogram of protection added to a vehicle reduces its speed, range, and payload capacity. Spall liners offer a favorable trade-off because they use lightweight textile composites rather than additional metal or ceramic armor. A full interior lining of aramid panels adds far less weight than the equivalent protection would require if engineers tried to simply make the primary armor thicker. For infantry fighting vehicles that need to carry a full squad of soldiers plus a crew, keeping weight down while maintaining survivability is one of the central design challenges, and spall liners are a key part of that equation.
Ongoing material improvements, like shear-thickening fluid treatments and hybrid fiber layups, are focused on squeezing more stopping power out of thinner, lighter panels. Even small reductions in liner thickness can free up interior space in vehicles where every centimeter of cabin room affects how many soldiers can ride inside and how quickly they can dismount.