Buff Proof Ink(BPI) is the first that GROG released and really, the name says it all... Very opaque, hard to remove, permanent ink with staining properties. The new BPI formula is improved with increased UV resistance, enhanced surface adhesion, and improved color opacity. Spray Planet offers the 5mm, 10mm, and 25mm BPI Squeezers as well as the BPI refill in death black.