Sapim makes nipples in nickel plated brass and in aluminum. All nipples are forged. Arguments in favour of a brass nipple are price and rigidity.
The strength/weight ratio is the principal argument for a 7075 alloy nipple. It is superior to all other makes. If a coloured anodized alloy nipple is selected it will guard against corrosion as well as look special.
The rounded design of the Patented Polyax nipple head reduces the stresses produced by axial and lateral forces (inherent in wheels with low spoke counts and crossings). Polyax nipples re-align themselves within a rim hole up to 9 degrees in a radial direction and 6 deg in an axial direction, making for a much superior fit. For this reason Polyax nipples are packed with all Chicken Cycle-Kit spokes.