Stretchy anti-radiation Silver-coated nylon skull cap with ear flaps is lightweight and breathes nicely. Comfortable enough to wear year-round while sleeping, thin enough to be worn under a conventional hat or all on its own. Stretchy, so it conforms to your head. Tested to shield 30 dB up to 10 GHz and beyond! Ear flaps can be tucked under to make a beanie shape if you prefer.