20 hour UniHeat heat packs (shipping warmers) activate quickly, usually about 5-10 minutes. The 20 hour UniHeat heat packs will achieve a higher maximum temperature when compared to the 30 and 40 hour shipping warmers. The 20 hour UniHeat heat packs reach their peak temperature in approximately 7 hours.
Under “Shipping Tips” found at the top of the home page, please see our complete guide on how to properly use and choose which UniHeat heat pack product is right for your shipping needs.
** 20 hour heat packs are not recommended for deliveries taking more than 15 hours. 40 hour is usually the best choice for next day shipments.