Hello, first of all, thank you for your interest. Our product is made of combed cotton fabric and is designed for daily use. It can be used in the sea or pool; however, due to the nature of the combed cotton fabric, it may become heavy and its flexibility may increase when it absorbs water. Therefore, especially for our users with small head circumferences, there may be looseness or gaps in the chin and neck areas. For sea and pool use, our knotted swim cap or three-band social swim cap models in our store may be more suitable. If you are going to use this product in water, you may need to use an additional bonnet or stabilizing accessory. Thank you for your interest.