Thermal insulation slows the transfer of heat, which naturally moves from warmer to cooler areas. While commonly associated with packaging, bubble wrap is sometimes perceived as an effective thermal insulator. However, this material often falls short as an effective barrier against heat flow. Understanding its limitations requires looking at how heat travels.
How Heat Moves
Heat can transfer through three mechanisms: conduction, convection, and radiation.
Conduction involves the transfer of heat through direct contact between materials, where thermal energy passes from one molecule to another. An example is a metal spoon heating up when placed in a hot liquid.
Convection is the transfer of heat through the movement of fluids, such as liquids or gases. Warm air rising and cooler air sinking creates a convection current, as seen when water boils in a pot.
Radiation is the transfer of heat through electromagnetic waves and does not require a medium to travel. The warmth felt from the sun or a campfire demonstrates heat transfer by radiation.
The Science of Trapped Air
Still air is an excellent thermal insulator because it is a poor conductor of heat. For air to provide significant insulation, it must be trapped, preventing its movement and inhibiting heat transfer by convection. Many effective insulating materials, such as fiberglass or foam, immobilize air within numerous small, disconnected pockets.
Why Bubble Wrap Isn’t an Insulator
While bubble wrap contains air pockets, a known insulating principle, its design has shortcomings. The plastic film, despite being a poor conductor compared to metals, still allows heat to conduct through its thin layers, reducing its overall insulating performance.
The air pockets within bubble wrap are often relatively large or can become interconnected, allowing for internal air movement and convection. This movement facilitates heat transfer, diminishing the insulating benefit of the trapped air. Additionally, if bubble wrap is not perfectly sealed around an object, air can move freely around and through it, further reducing its insulating effect.
Clear plastic, like that used in standard bubble wrap, is largely transparent to infrared radiation. This means radiant heat can pass directly through the material with little impedance, especially with a notable temperature difference. Effective insulators often incorporate reflective surfaces to block radiant heat, a feature typically absent in clear bubble wrap.
What Makes a Good Insulator?
Effective thermal insulators possess characteristics that enable them to combat all three forms of heat transfer. They feature numerous tiny, disconnected air pockets that prevent convection by restricting air movement. Materials like fiberglass, foam, or wool exemplify this design, trapping air efficiently. Good insulators are also made from materials that are poor conductors of heat, limiting the direct transfer of thermal energy through their solid structure. Many effective insulators also integrate reflective surfaces, such as foil backings, to block radiant heat by reflecting it away rather than absorbing it.