As the quarterback’s cleats pull away from the turf, a microscopic splash of black granules and sand follow him.
On the surface, the field appears to be a swath of solid green, but between the grass blades hide these small particles. Like topsoil underneath a grass field, these particles of sand and rubber support gameplay unseen.
What is infill?
The combination of sand and rubber pellets is called infill. CenturyLink Field installed new turf in 2016 and filled it with a combination of infill sand from Washington Rock Quarries and tiny pellets of recycled rubber.
The sand and rubber pellets were distributed over top of the field with a special machine. Another machine then swept the surface of the field and brushed the infill into place around the grass fibers.
Infill is essential in keeping players safe.
Infill is as essential to synthetic turf as topsoil is to real grass. Here are some of its benefits:
- Grass Blade Support. The infill helps the soft synthetic blades stand up straight.
- Field Stabilization. Have you ever tripped on a carpet with ripples in it? That probably happened because there was nothing to keep the carpet in place. Infill weighs the synthetic turf carpet down and ensures that the carpet doesn’t ripple.
- Injury Prevention. The right combination of rubber and sand helps to support players’ bodies and cushion falls.
- Drainage. Where does rain go when it falls on the field? Synthetic fields typically have a drainage system underneath the turf. Infill, especially infill sand, helps drain water away from the field into this system.
Infill is so important to player safety that the NFL certifies it before every game.
Getting the depth of infill and ratio of sand and rubber just right is essential to keeping athletes safe. In one study, the American Orthopaedic Society for Sports Medicine found that too little infill led to a harder playing surface and more injuries. Infill’s direct role in player safety is why it has to be certified before every game.
Seventy-two hours before each game, NFL field certification experts inspect the field, including the infill depth. The NFL Field Certification webpage explains that “the league measures infill depth at 40 designated areas around the field to make sure that it isn’t too soft or too hard and that the infill is distributed evenly. In spots that are uneven, crews can add, remove or smooth the infill.”
What makes infill sand different from other sand?
Infill sand has to be extremely uniform, dry, and clean. Washington Rock’s infill sand is vigorously washed to make it as clean as possible. Then it is kiln dried. The sand is funneled into 3,500-pound Super Sacks, which are then placed on pallets and loaded on trucks for delivery.
At the field, a forklift raises each Super Sack, one at a time, above a large broadcast spreader seated on the back of a cart. The bottom of the sack is cut open with a long-handle knife, and the sand pours into the spreader. Then the cart drives the entire field, broadcasting sand over top of the turf.
Learn more about our turf and track products, including infill sand, on our Sports Field Products page.