The UV Replacement packs of 5 or 10 filters allow the active GoPro Hero 3 user to use and abuse their favourite filters without the need to repurchase a full kit. This -20UV filter reduces UV aberrations/pollution below 18 metres. As light is limited at this depth then filtering can be very problematic. It only slightly reduces available light but stops the pollution problems. These filters will only work with the Formatt-Hitech GoPro Hero 3 holder.