The difference between bonded and unbonded insulation is important because different products work better at different temperatures. For example, most insulated windows are made of two layers. The bottom layer is typically an aluminum extrusion bonded to a steel core with an adhesive. The interior surface is covered with a plastic film called polyethylene that is extruded as well, so the two layers meet in a sealed sandwich: the aluminum on top, the aluminum on bottom.

The purpose of the two-layer construction is to make sure the window stays rigid and doesn’t leak air. In cold weather such windows are very good insulators, but they are also stiff and hard to open and close. In hot weather they let in lots of heat through their relatively thin plastic films, letting hot air into the house but not letting it out again.

In contrast, some windows are made of unbonded insulation sandwiched between two layers of aluminum foil. This way you can add or remove insulation according to your needs: if you want to keep cool, you can add more foil; if you want to keep out heat you can remove some foil. This gives your windows flexibility and makes them easier to open and close in both cold and hot weather.

This kind of window has become popular for many

Insulation used to be called “bonded” because it was usually made out of sheets of a stiff paper, which were then coated with a glue that bound the layers together.

Nowadays there are two kinds of insulation: unbonded and bonded. Unbonded insulation is what you’re familiar with from your house; it’s just a thin layer of paper wrapped around foam or plastic or some other insulating material. Most of the insulation in your home is unbonded.

Bonded insulation is what you’d call “bulk.” It consists of a rigid structure that holds insulating materials in place. The most common structure is pipe, like ductwork, but they also make it out of pieces of lumber or plywood.

The advantage of bonded insulation is that it’s cheaper and easier to use than unbonded. The disadvantage is that if you have any kind of structural damage or leak, you’re much more likely to lose your insulation than with unbonded insulation.

Hardiebacker is a website that generates a graph of the energy efficiency of buildings by year, state and type. The data comes from EnergyStar and the US Department of Energy. The graph also shows what percentage of houses are heated with oil or gas, if they are built with any type of insulation. For example, in 2014, nearly one quarter of all new US homes had no insulation at all. None!

Bonded Insulation

Insulation products manufactured to be installed between two layers of drywall, stucco or concrete. The most common form is fiberglass batts that must be cut into manageable shapes before installation.

Unbonded Insulation

No bonded insulation product is required by building codes or mandated by the government. Unbonded insulation has become much more popular in recent years because it is cheaper to install than fiberglass batts and contractors are not required to install it for customers. Unbonded insulation is used for sound deadening purposes and does not provide thermal comfort benefits as fiberglass does.

The most common job in the world is doctor: heal people, cure diseases, and make them feel better. The most common profession is lawyer: provide legal services to people who need them. There are lots of jobs in between, but they’re not as common; there are fewer jobs than professions.

Bonded insulation systems provide a very high level of safety and comfort for people like doctors. But unbonded systems offer security and peace of mind for people like lawyers or accountants or plumbers or teachers or journalists or firefighters or bankers.

We usually think of insulation as a material – wool, foam, fiberglass or rockwool – that is attached to the surface it is supposed to insulate. In reality most of the time, the material is actually bonded to the surface it is supposed to insulate. If you use properly designed and installed insulation, this does not matter. But if you don’t, it matters a lot.

Bonded insulation can be a serious fire risk. For example, in 2009 an insulation fire in Colorado Springs killed three people, injured seven others and damaged six buildings. The fire started when air leaked into the attic through a gap between the insulation and the roof sheathing; the attic was made of un-bonded insulation.

There are a lot of ways to insulate a building. The most common is to use rigid foam insulation, which is usually made from recycled products and is usually installed by a professional.

The other common way to insulate buildings is to use loose-fill insulation, which uses compressed paper fibers or small pieces of cellulose. Both methods have advantages and disadvantages.

Loose-fill insulation has been around for longer than rigid foam, but it’s not quite as energy efficient, and it has some potentially dangerous environmental impacts.

Bonded insulation uses an expanded-polystyrene product that’s more like foam than paper, but it doesn’t expand much at all when hot water hits it.”

The difference is the same as the difference between a good carpenter and a bad carpenter. It is a question of trust. The good carpenter says, “I’m going to do this right, so I’m going to use the best materials.” The bad one says, “I can buy these cheap because they’re home insulation.”

The professionals not only use better materials; they understand how to make them work. And they know what your goals are.