The watertightness of the swimming cap varies according to the model:
The material of the embossed cap is waterproof, it protects the head from splashes above water, but it isn't watertight. It primarily provides comfort and therefore does not grip the head, which means water can pass under the cap.
PLEASE NOTE: NO SWIMMING CAPS ARE 100% WATERTIGHT. THE WATER FLOWS UNDER THE CAP, ESPECIALLY AROUND THE EARS