A self-contained, disposable, single-use heat generating apparatus, comprising: a heat generating pack comprising: a first bag layer having a first surface area; a second bag layer having a second surface area, said second bag layer being fixed to said first bag layer, such that said first bag layer and said second bag layer defining a pouch there between; a heat generating agent disposed in said pouch, said heat generating agent arranged and configured to consume air at a predetermined air consumption rate in an exothermic reaction; and at least one of said first surface area and said second surface area comprises an air permeable surface area having a predetermined airflow rate at which air is introduced to said heat generating agent, said predetermined airflow rate being arranged and configured to be less than said predetermined air consumption rate such that said heat generating agent remains substantially evenly distributed within said pouch, characterized in that the agent comprises a) 35 - 50 % by weight of iron powder, b) 25 - 45 % by weight of water, c) 10 - 14 % by weight of water-retaining agent and d) 4.5 - 6 % by weight of salt and the heat radiating from the heat generating apparatus ranges from 39 - 45°C. a heat generating pack comprising: a first bag layer having a first surface area; a second bag layer having a second surface area, said second bag layer being fixed to said first bag layer, such that said first bag layer and said second bag layer defining a pouch there between; a heat generating agent disposed in said pouch, said heat generating agent arranged and configured to consume air at a predetermined air consumption rate in an exothermic reaction; and at least one of said first surface area and said second surface area comprises an air permeable surface area having a predetermined airflow rate at which air is introduced to said heat generating agent, said predetermined airflow rate being arranged and configured to be less than said predetermined air consumption rate such that said heat generating agent remains substantially evenly distributed within said pouch, characterized in that the agent comprises a) 35 - 50 % by weight of iron powder, b) 25 - 45 % by weight of water, c) 10 - 14 % by weight of water-retaining agent and d) 4.5 - 6 % by weight of salt a first bag layer having a first surface area; a second bag layer having a second surface area, said second bag layer being fixed to said first bag layer, such that said first bag layer and said second bag layer defining a pouch there between; a heat generating agent disposed in said pouch, said heat generating agent arranged and configured to consume air at a predetermined air consumption rate in an exothermic reaction; and at least one of said first surface area and said second surface area comprises an air permeable surface area having a predetermined airflow rate at which air is introduced to said heat generating agent, said predetermined airflow rate being arranged and configured to be less than said predetermined air consumption rate such that said heat generating agent remains substantially evenly distributed within said pouch, characterized in that the agent comprises a) 35 - 50 % by weight of iron powder, b) 25 - 45 % by weight of water, c) 10 - 14 % by weight of water-retaining agent and d) 4.5 - 6 % by weight of salt a) 35 - 50 % by weight of iron powder, b) 25 - 45 % by weight of water, c) 10 - 14 % by weight of water-retaining agent and d) 4.5 - 6 % by weight of salt and the heat radiating from the heat generating apparatus ranges from 39 - 45°C.