Note: Head circumference is less than 26 inches and greater than 23 inches. | high protection - damping 10 MHz 3 GHz 30 - 55 db | POWERFUL PROTECTION: Shielding performance Max 99.99% (1.5GHz) /Shielding: LF(Low frequency electric fields) & HF(High frequency electric fields).Unique radio frequency shielding fabric in lining,Shields RF from wi-fi, cellphones, smart meters. | Raw materials: 25% silver fiber, 75% nylon spandex. Machine wash cold. Air dry. Do not bleach. Recommended for daily usage. Very safe for people's body. | The EMF radiation cap is an ideal helmet to protect the head area. It can significantly reduce the high frequency/RF EMF cell phone generated by Wi-Fi modem, home and automotive Bluetooth devices, smart meters, cell phone towers, microwave ovens, cordless and other signal sources, as well as the low frequency/RF EMF cell phone from wires, electrical boxes, household appliances and high power transmission lines. Frequency electric field. Perfect everyday wear, indoor and outdoor activities.