A sheet of glass provides the best protection against sunburn at the beach because it effectively blocks UVB rays, unlike cloudy days or simply turning your body frequently.
The best option to shield you from sunburn when at the beach is a sheet of glass between you and the Sun. A cloudy day can still allow harmful UVB rays to pass through, and frequent turning doesn’t provide continuous protection against UV radiation. The sheet of glass typically blocks most UVB rays, providing more effective protection.
For further protection, using sunblock with a high SPF that guards against both UVA and UVB radiation, or wearing sun protective clothing with a UPF rating, is advisable to mitigate the risk of immediate skin damage and long-term issues such as skin cancer.