Truly a one size fits all, thanks to our design innovation team. Can be adjusted large enough for your head (up to 22"), or small enough for your neck (as small as 8"). The back concealed pocket holds one frozen CoolPak strip against the base of your head - or when worn around your neck, the CoolPak can be positioned at the back of neck - or at front, to cool blood at your carotid arteries. Positioned at the base of your head, the CoolPak helps cool the blood enroute to your brain, where overheating occurs! The Science Cooling the neck has been shown to help improve performance, reduce sweating, and enhance the feeling of comfort1,2. Even this small area of the body will yield some surprising benefits from cooling. Surface cooling depends primarily on how much surface area you can cover, where more is better. However, there are a few small areas on the body which provide unique responses to cooling. The back of your neck is one of those areas. The palms of your hands is another. Read more about palm cooling in our "CoolCuffs" section. References: 1. Yang Zhang et al. Cooling on Soccer Performance. Monten. J. Sports Sci. Med. 3 (2014) 1: 17-22 2. Tyler, C. J., and C. Sunderland. Neck Cooling and Running Performance in the Heat Med. Sci. Sports Exerc., Vol. 43, No. 12, pp. 00-00, 2011 3. Ruddock, A. et al (2014). Effect of hand cooling on body temperature, cardiovascular and perceptual responses during recumbent cycling in a hot environment. Journal of Science and Cycling, 3 (2). Features: Truly a one size fits all Can be adjusted large enough for your head (up to 22"), or small enough for your neck (as small as 8") The back concealed pocket holds one frozen CoolPak strip against the base of your head CoolPak helps cool the blood enroute to your brain, where overheating occurs CoolPak can be positioned at the back of neck - or at front, to cool blood at your carotid arteries