A BIAB manicure uses Builder in a Bottle, a gel-like nail polish, which is applied as an overlay on your natural nails. It works very similarly to a normal gel polish, but as it has a thicker consistency it dries as a strong and durable layer - so you don't have to worry about chipping your brand new nails. It's gentler than acrylic, but thicker than regular nail polish and gel polish. The protective shell it creates over nails is designed to encourage natural nail growth and strength.