Infrared is a direct form of heating whose source is the infrared emitter that radiates energy. The energy is absorbed by the product directly from the emitter, not through an intermediate medium. The energy converts to heat when it is absorbed by the product. With convection heating, the air must be heated, which then heats the product.

Infrared energy is dispersed from its source in much the same way as visible light. Exposed product surfaces easily absorb the infrared energy and become heated, so heating effectiveness is related to line-of-sight between the source and the product. Depending on the product's coating and/or substrate material, the heat is further thermally conducted.

The ability of the product to absorb energy also is known as its emissivity. A theoretical body that absorbs all energy is called a black body, which has an emissivity of one. A highly reflective body would have a low emissivity value, approaching zero. Reflectivity is the inverse of emissivity.

The potential of a product to become heated with infrared is related to the following:

• Watt density (total output power) of the source.
  
• Wavelength (temperature) of the source.
  
• Distance from the source to the product.
  
• Reflective characteristics of the oven cavity.
  
• Air movement and temperature in the oven.
  
• Length of time the product is exposed to the source.
  
• Ratio of exposed surface area to the mass of the product.
  
• Specific heat of the product.
  
• Emissivity of the product.
  
• Thermal conductivity of the product.