GEPULY 4-Pack Camera Lens Filter Kit for Gopro Hero 12/11/10/9 Black: CPL, ND16,
ND16 Filter:Neutral Density filter reduce light to decrease chance of overexposure, Polarizer filter increase contrast while eliminating reflection and glare. ND16 allows 1/16 of the light to pass through, which is about 4 shutter speeds.