Riemann p20 once a day sun filter spf20 3 pack p20 are designed to ensure one application a day is sufficient keeping the time spent reapplying sun protection to a minimum once a day application means a little goes a long way making p20 more economical than other sun preparations that need to be re applied regularly during the day superior water resistance the once a day formula is proven to remain effective even after frequent swimming in fact p20 has been categorised as very water