The argument for these is that the cost of carrying one is close to zero. A folded foil sheet takes less room than a bandage and helps retain body heat where someone is exposed, wet or in shock while help arrives. They tear easily and are effectively single use, so treat them as a consumable and replace after any incident. Check the folded pack has not split. See first aid kits, first aid bags and kit refills.

Emergency blanket displayed in a bright modern first aid setup with kit, checklist and emergency supplies for heat retention.
Emergency Blankets for First Aid

Shop emergency blankets for first aid kits, workplaces, vehicles, outdoor activities and emergency response.