Note: The child’s head circumference is less than 21 inches! Small for children??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.