Once the grass is all stapled and glued down, they fluff it and start infilling it. First they rub in 1/4 to 1/2 inch of sand. On top of that, goes same amount of black rubber grit. This adds a lot to the spongy-ness and realistic feel to the grass as you walk on it. Going to ask today if that rubber needs to be refilled in once in a while.
Here are the nails: big bad boys...
Even better, the rubber grit is made 100% from recycled tires, so that adds another plus to synthetic lawn installation. No water, no fertilizer, no weeds, no mowing. And reuses rubber tires which are a terrible product to put in land fills as pure waste. Costs a lot, but lasts 20-30 years, if not abused.