[yuhaoyang]

the more they're polished the less irregular their surfaces are on a microscopic level (ie. the same reason why you wax your car, so that light refects more evenly), which makes a difference in areodynamics on such a small and light projectile(but doesn't make much of a difference on... your car =p).
Bioval BBBmax looks like glass, and despite me never being able to get any, I would suspect that they are extremely well polished and smooth.