Heater

A warming device, comprising:

• a topsheet configured to be located close to a skin of a user;
• a backsheet configured to be located far from the skin of the user;
• and
• a heat generating element interposed between the topsheet and the backsheet,
• wherein the heat generating element comprises an oxidizable metal, a carbon material, an electrolyte, and water,
• the heat generating element is configured to generate vapor from the heat generating element itself as heat is generated,
• the topsheet is a breathable fiber sheet including fibers comprising at least a polyethylene terephthalate resin,
• the topsheet has a multiple layer structure comprising a first fiber layer and a second fiber layer,
• the first fiber layer is provided at a side far from a skin of a user when the warming device is used,
• the second fiber layer is configured to contact the skin of a user when the warming device is used,
• the first fiber layer comprises first fibers and third fibers,
• the first fiber layer is the only fiber layer that comprises the first fibers, and the first fibers have a fiber diameter of more than 15 μm in plan view as measured by observation under a scanning electron microscope, and
• the second fiber layer comprises second fibers having a fiber diameter different than the first fibers.