In a rare example of the government using words efficiently, the Department of Energy provides an excellent explanation of the role of insulation.
Heat, DOE says, has a natural inclination to migrate to anywhere there is a cooler temperature. Therefore, in winter, heat wants out; out of heated living areas into the colder walls, basements, and if it can get there, outside. In the summer it wants in, sneaking through walls, cracks, and holes into the cooler air in or under a building. Therefore, the purpose of insulation is to provide resistance to the flow of heat which should, ideally, increase the efficiency of our heating and air conditioning systems and end the drafts and uneven temperatures that are a by-product of heat flow.
Early people understood, on some level, the need to insulate themselves from the weather. It's hard to find a better example of insulation than a cave or the mud hogans built by Native Americans. Early settlers kept warm in houses made of hay bales, adobe bricks, or logs carefully chinked with mud. But somewhere along the line we got pretty stupid about insulation.
Almost anyone who has restored a house built in the 1800s or 1900s will attest that those were generations more concerned with form than function. Pretty gingerbread, architectural shingles, coynes and medallions abound, but the actual construction tended toward clapboards on the outside of the framing, horsehair plaster on the inside, and nothing in between. Ceilings were actually stained in the pattern of the wooden plaster lathe above by heat escaping into the attic and out through the roof.
When we did wise up to the need for insulation there weren't a lot of products out there. That newspaper which solved an old mystery when found in a wall? Insulation!
Early products tended to settle in the walls, attract rodents; burn merrily if given the chance, and cause health problems and on top of all that, didn't work that well.
Even houses built in the third quarter of the last century left a lot to be desired in the way of insulation and there were some serious misses such as the use of urea formaldehyde foam which made a lot of people sick.
Today there are many alternatives, good alternatives available. Fiberglas, cellulose, polystyrene, polyurethane and as me mentioned yesterday, soy, are all used as insulation in several forms. Batts, blankets, loose fill, and low-density foams all limit air movement and some of the foams contain gases that further inhibit air flow. And air itself is a good insulator if it can be made to stand still.
Some products for new home construction are more than just insulation; they are complete building and insulation systems. Products for retrofit are more limited, mainly because of accessing the places needing insulation. But sometimes even small measures can make a big difference.
It's an exhaustive subject and it might be a toss-up whether reader or writer will get bored first, but we will talk about a few topics in the next little while then return to the topic many times in the future.