Is Aluminum Foil a Good Insulator? Why It Works Explained

Aluminum foil is used to keep food warm, to keep soft coolers cold, and even in housing insulation and space blankets for hikers. But being a metal, doesn't that mean it's a good conductor of heat?

Is aluminum foil a good insulator? If so, how exactly does it keep your food from getting cold or your house from getting warmer in the summer?

In short:

Aluminum foil is a great insulator when used properly, but a poor insulator when used incorrectly. It's a great heat reflector, and since air/water can't pass through it, it also stops heat from evaporating and convecting. But it's a good conductor of heat, so if it's in direct contact with something, it won't insulate well.

Aluminum is both a good thermal insulator and a poor thermal insulator (or a good thermal conductor). How can this be true?

Don't worry, it took us a little while to understand the concept as well, but I'll explain it briefly, and understanding it will help you get the foil right.

Heat is transferred to or taken away from objects in 3 main ways.

When one object touches another, heat moves through it (think a saucepan on a hot stove).

Aluminum foil is a great conductor of heat, which means it's a poor insulator when it's in direct contact with something hot. It's also thin enough that heat can pass through it very easily when it's in direct contact.

This is the type of heat transfer that aluminum is not good at preventing.

Heat can flow from one area to another via liquid or gas (think a hair dryer blowing hot air across a room or pushing hot water to the other side of a cold bath)

Aluminum foil stops hot water/gas from evaporating from food because water and air cannot pass through it. This prevents a lot of heat loss through convection.

Heat can be moved electromagnetically through radiation (think of the sun sending heat to us through the vacuum of space, or a laser pointer sending light far away)

Aluminum foil is also a great reflector of radiant heat, in fact, one of the best materials out there. As a result, it reflects almost all heat energy back to its source, keeping your food warm or keeping the sun's heat out of your house in summer.

This is the amazing type of heat transfer that aluminum does when it comes to a stop.

While aluminum is a metal and thus conducts heat, it actually has other properties that make it very effective at keeping food warm.

Aluminum has a high emissivity, or it is a magical heat radiation reflector. Everything with a temperature above absolute zero loses heat through thermal radiation.

The hotter the food, the more heat is lost through radiation.

But covering food with aluminum foil will reflect almost all of the radiant heat back into the food, keeping it warm.

One of the main ways food loses heat is through evaporation.

Food contains a lot of water, and when that water evaporates and leaves the food, it takes a lot of heat with it.

Because water and air cannot pass through the aluminum foil, which means it locks moisture in warm food and keeps food warmer for longer.

The aluminum foil is rolled to create many small air gaps. As we learned in the article, Styrofoam is a great insulator, the air is a great insulator, and heat is difficult to transmit through air. Therefore, creating these air pockets improves insulation.

If you double-layer the foil then you get multiple air pockets which work better.

Because of its emissivity (or reflective properties), aluminum insulation is often used on roofs and walls of homes to keep them warm in winter and cool in summer.

It works by reflecting most of the infrared heat that tries to enter the house in summer or leaves it in winter.

It's not the best insulator by itself as it only really blocks radiant heat, but when combined with another insulating material such as Styrofoam or fiberglass, aluminum reflects heat radiation while another insulating material prevents heat conduction.

In general, aluminum insulation for homes is like bubble wrap, with an inner or outer layer of aluminum (or both) and a plastic bubble in the middle.

The air bubbles act as insulation to block airflow and prevent heat transfer by convection and conduction, while the aluminum layer blocks heat radiation.

A space blanket is a special emergency blanket that is often carried by hikers or used by marathon runners to keep warm.

They're super light, pack really little, and if the weather changes, they'll keep you warm enough to get through the night.

The Space Blanket is made from a combination of plastic and aluminum, so it's strong enough not to tear, yet reflective enough to trap some heat.

Regular blankets and sleeping bags keep you warm by using many small air pockets to prevent conduction and convection of heat. That's not how space blankets work.

The space blanket only really reflects heat radiation back to your body.

So sticking a space blanket to your skin won't do much, as the cold air outside will cool the blanket and thus your skin.

Instead, you want to leave some air space between you and the space blanket. To do this, hang it on yourself as loosely as possible. The blanket itself will get cold, but if it's not touching you, it won't catch you.

Instead, it invisibly reflects heat radiation back to your body and stops cold winds from blowing through your clothing and onto your skin.

These two features will help you stay warm enough to survive. It won't keep you warm and warm like a duck blanket at home, but it will work well and you shouldn't freeze.

The insulation principle of aluminum foil has been introduced in detail above, if you want to buy aluminum foil, please contact us.

PENGYUAN is a professional custom aluminum foil manufacturer in China. We have 3 vacuum coating machines and 8 PE extrusion coating production lines, guided by the 6S management system. As the largest extruder coating base in China, the company has obtained ISO9001, ISO14001, ISO45001 production standards for the whole system. Pengyuan is committed to becoming an advanced provider of energy-saving new materials and solutions.