The FDA allows two water-resistance claims: 40 minutes and 80 minutes, tested using the FDA-recognized ISO 16773 protocol where subjects are immersed in water for the stated period before SPF is re-measured. An 80-minute claim requires a stronger film-forming polymer system and is considerably harder to achieve. Your cosmetic chemist needs prior experience with whichever claim you're targeting.
Read the full guide on how to find a formulator for waterproof sunscreen spray →