Versatile Design: The silver fiber lining can be worn alone or paired with other hats, offering more options. Lightweight and Breathable: Made with comfortable and breathable nylon (containing silver fiber) fabric, ensuring you stay cool and comfortable. 3G/4G/5G Protection: Effectively protects your head from electromagnetic radiation while maintaining a stylish look. Provides protection anytime, anywhere, while remaining discreet. One Size Fits All: Height: 22cm/8.66 inches; Head circumference: 58cm/22.83 inches; Elastic head circumference: 60-64cm/23.62-25.20 inches. Suitable for all head sizes, one size fits all. Suitable for: Shielding cell phone towers, microwave signals, telephones, meters, , military broadcasts, etc. Contains anti-static fabric, wireless instrument shielding, and electronic textiles, reducing electromagnetic (EMP) and electromagnetic interference (EMI) radiation.