Drag is every swimmer’s worst enemy, one that yields only grudgingly to strength, conditioning and determination. Speedo is giving top-tier swimmers a new weapon in that age-old fight, one it claims pushes the frontiers of swimwear.

Speedo says its Fastskin3 swimsuit, cap and googles are the most streamlined ever. The company, which invested four years and 55,000 man hours developing the swimwear, claims it produces a 16.6 percent reduction in full body passive drag. It is the biggest advance in swimwear design since the International Swimming Federation banned polyurethane body suits two...