UST Reusable Hand Warmer with Environmentally Friendly, Compact Design and Instant Activation for Hiking, Camping, Backpacking and Outdoor Survival DIMENSIONS: 4.1 H x 3 W x 0.8 D weighs 2.3 oz each VERSATILITY: When the heat runs out, the warmer can be rejuvenated by soaking in boiling water and stored in small areas such as a pocket or a backpack RELIABLE: Once activated, the hand warmer provides heat for up to 2 hours making it ideal to have in emergency situations where heat is needed CONVENIENT: Heats up to 130 degrees F in just 15 seconds allowing for nearly instant access to extra warmth MATERIALS: Sodium acetate and water are activated by bending a metal disk inside the pouch