Why are several of thin layers better for warmth than one thick one?

Answer 1

Keeping warm as a mammal is all about trapping the heat we generate through respiration.

Reptiles have to sunbathe to raise their body temperature and kick start their metabolism sufficiently to be able to function efficiently and at speed. Mammals, birds and (almost certainly) dinosaurs are/were warm blooded and produce their own heat.

If you had a beaker of cold water you couldn't make it warm by giving it several layers of insulation. You can, however, keep it cool or if you replace the cold water with warm water you can keep that warm.

Insulation works by trapping a layer of air between layers of a solid substance such as cotton. If you have no insulation the heat generated by a body radiates from it as infrared radiation and directly heats the air surrounding the body through kinetic energy (air particles being struck by the vibration of the particles in the skin). These warmer air molecules then move away due to convection taking heat energy with them.

With one layer of insulation some of the radiated heat energy is reflected back but much of it still escapes. The layer also serves to trap some air providing a slight buffer and preventing some loss of heat through convection. Ironically, however, solids conduct heat better than gases (there being more particles per unit area and it being easier to transmit the kinetic energy) through conduction.

With multiple thin layers there are more surfaces for infrared radiation to reflect back off and each trapped layer of air serves as a further buffer against conduction and convection.

The best form of insulation would incorporate a vacuum layer between highly reflective materials. The vacuum would ensure that no conduction or convection could take place (as there would be nothing to transmit the kinetic energy) and the reflective materials would reflect the infrared radiation back to the body.

Answer 2

Multiple thin layers trap air in between them, creating insulation that helps retain body heat. This trapped air acts as a barrier against the cold, while also allowing for better moisture management. In contrast, a single thick layer may compress and reduce its insulating properties.