See this link for a study that was done to see what types of caps affect speed. I dont know
why they tried a bubble cap as they are a hair/ear care fitness swim cap and not a race cap. Also they tried a lycra cap and those are not as fast either as the fabric offers more friction. They were surprised that no cap was as fast as the others. Why they did not try the race latex or silicon I dont know. They used three swimmers for lap times and push off distance from the wall for the results. I dont really think any cap really would slow a swimmer that much unless they were world class.
www.drjreid.com/.../Swimcaps change swimmer speed.pdf
