UniHeat heat packs have an activation period in approximately 40-50 minutes. These are cooler, and generally safer than 40 hour heat packs. These heat packs reach their peak temperature in approximately 24- 26 hours. These warmers are useful for shipping insects and plants, and can be used in conjunction with Phase 22 packs for shipping reptiles and amphibians.
Please make sure that there is insulation or packing material between a cool pack and live organisms.