Perfect for: Travel, home, office, shopping, outdoor activities, and everyday wear. Its electromagnetic radiation shielding material significantly reduces the risk of exposure to harmful wireless radiation outdoors. 360° Radiation Shielding: The electromagnetic radiation shielding lining effectively reduces high-frequency radio frequency and millimeter-wave radiation, covering the entire inside of the hat. Ideal Fabric for Electromagnetic Radiation Protection Hat: Outer fabric: 60% cotton, 30% nylon, 10% wool; Lining: 42% silver, 53% cotton. Suitable for: Shielding cell phone towers, microwave signals, telephones, meters, , military broadcasts, etc. The anti-static cloth, wireless instrument shielding, and electronic textiles reduce electromagnetic (EMP) and electromagnetic interference (EMI) radiation. One Size Fits All: Hat circumference 22.83/23.23 inch/58/59 cm, made of elastic fabric, suitable for all head sizes, one-size-fits-all design.