KOOLSUN Flex kids sunglasses are sturdy and flexible. The KOOLSUN Flex kids sunglasses come with a handy strap which you can easily fasten and unfasten. The Flex kids sunglasses are all equipped with strong polycarbonate glasses. These blocks 100% of UVA and UVB radiation this is also called UV400. All glasses are CE category 3. This means that the light intensity is reduced by more than 80%. This is necessary in order to be able to see comfortably in sunny weather.