Never use any powder you come by… always use lifting chalk. The same chalk used by rock-climbers.
That means no baby powder, no corn starch, no flour or any other white powder you could think of (cocaine would be a costly, ineffective alternative!).
Lifting chalk is made of magnesium carbonate (MgCO3). It absorbs sweat and raises friction between your skin and the bar. (Can also be sprinkled on the floor for a better adhesion; most gym owners will hate you…).
Chalk offers the ultimate grip: essential when you lift heavy. Get some and use it!