The On The Run Hard To Buff Ink is a deep black and very strong alcohol based ink. It is instantly waterproof. The ink is also fade proof. The Hard to Buff marker features a great pump action system. The 15mm nib is replaceable. Waterproof and long lasting. REFILLABLE. This is the pocket version of the regular OTR Hard 2 Buff marker. It has the same nib and a shorter body which makes it easily fit in for pocket.