The Chill-Its 6687 Dry Evaporative Cooling Vest offers immediate and dry cooling relief that lasts up to three days. With its exclusive dry evaporative technology, this cooling vest keeps the wearer completely dry and comfortable, as opposed to other cooling vests on the market that require soaking and get you wet. To activate, simply fill the vest with 13.5 oz to 15.5 oz of water for immediate and long-lasting cooling relief. No refrigeration or gels necessary! The cooling process can last up to three days depending on humidity and heat levels. High humidity levels can slow down airflow and may reduce cooling abilities.