How Does Insulation Work?

OK. This is a new blog.

Just got an email from a
high school student. He
writes:

Hello,

my name is Name Withheld and
I attend Name Withheld High
School. Three of my friends
and I are doing a science
project on how we can make used
coats warmer.

We saw you gave advice on how
to stay warm in the winter.

My friends and I were wondering
if you could tell us how
insulation works and also if you
have any ideas of what we could
fill a coat with.

Please keep in mind that young
teens should be able to re-create
our project themselves. We also
need materials that are in common
households. I hope you can help
us!

Thanks,

Name Withheld

The student refers to an article
I wrote:

12 Tips to Help You Choose Warmer Clothes

Here is how I replied to him:

Hi FirstName,

Good to hear from you.

How does insulation
work?

I suppose I should answer
another question first.  How
does heat transfer from one
place to another?

Knowing how heat transfers
is essential to understanding
insulation.

Heat transfers in 3 ways:

1. Radiation.  You feel this
   when getting too close to a
   fire.
2. Conduction.  This can cause
   you to burn your hand when you
   touch a hot stove.
3. Convection.  You feel this when
   you open an oven door and you get a
   hot blast of air in your face.

Basically, the 3 ways heat transfers
from one place to another are quite
simple:

1. Radiation.  Radiation travels
   through the air.  McDonald's uses
   light bulbs that emit infrared light
   to keep hamburgers and french fries
   warm.  You've probably seen this.
   
   Think of the red lights that the
   french fries sit underneath.
2. Convection.  Anytime you feel
   a warm or cold patch of water when
   swimming in a lake, you are
   experiencing convection.
3. Anytime you touch something
   warm, such a potato that has just
   come out of the oven, you are
   experiencing conduction.

Back to the original question.  
How does insulation work?

Mostly by breaking up convection
currents into little tiny air
bubbles.  The smaller the bubbles,
the harder it is for the air to
travel far.

That's it in a nutshell.

So how would you make old coats
warm again?  Probably by repairing
them and stuffing them with insulation
again.

You need a cheap source of insulation.

Ground up leaves would work but are
useless when wet.

Polar fleece would be better but might
be a bit expensive.

A rather interesting solution might be
to take some old jackets, cut them up,
and use them to insulate other old jackets.

In other words, do some triage.

If a jacket is beyond helping, you
cut it up to better serve the jackets
that can still be salvaged.

This way, you know you are using
jacket-like material and are less
likely to get into trouble.

Keep in mind that almost all light
airy materials will work to some
degree but not all materials
are safe for this purpose.

For example, some materials
deteriorate quickly, others
form mold and other undesirable
things. Still others, are
useless when wet.

So, you have to choose carefully.

I'd say, just guessing, that old
jackets might work to fill other
old jackets.  However, you are
going to want to launder the
jackets before doing anything.  
Otherwise, the jackets could
prove a bit funky.

Ask your teacher what this means
if you do not know.

Kind regards,

Ed Abbott

In looking over and lightly
editing the two letters, I
realize that I probably could
have given a better explanation
of how insulation works.

I said that insulation breaks
the air up into small air bubbles.

This is true.

However, it is not much of an
explanation.

In general, any material that is
light and prone to float in the
air is probably a fairly decent
insulator.

For example, bird feathers are
very light and make great down
jackets.

I mentioned in the letter that
you could use leaves. This is
probably true. You could use
leaves and pine needles.

However, you'd have to find a way
to keep them light and try.

Manufacturers of down jackets refer
to something called loft.
Basically, that's the ability of the
material to re-inflate itself after
it gets wet.

I doubt that wet leaves would ever
re-inflate and they would be very
difficult to keep dry.

One of the beauties of wool is that
it does not deflate when wet.
Therefore, it keeps you warm, even
when wet.

Fur, in general, has this quality.

For example the Inuit of Alaska,
often called the Eskimos, used
Caribou fur to keep warm. Caribou
fur is warm, even when wet.

So, this leads me to my explanation
of how insulation forms little air
bubbles. Basically a good insulator
is light because it is mostly air.

• Wool is mostly air
• Caribou fur is mostly air
• Blown-in attic insulation,
  made out of treated and recycled
  newspaper, is mostly air
• Fiber-glass insulation that
  you put in your walls is mostly
  air
• Polar fleece is mostly air
• Bagged leaves are mostly air

An interesting aspect of the
lives of the Inuit is that they
made temporary traveling shelters,
called igloos, out of snow.

Snow, especially when dry and freshly
fallen, is mostly air. This is especially
true of snow that falls at low temperatures.

Snow that falls at low temperatures
is known as dry snow. Dry snow
is especially light and dry with
air.

In short, good insulators typically
have lots of little tiny spaces to
trap air bubbles.

That's how good insulators work. They
form little air pockets, thus breaking
up the transfer of heat away from your
body or away from your house.

The heat can still escape, but it escapes
much more slowly because it has to travel
across so many tiny air bubbles.

Think of it this way. If a
calorie of heat, which is,
basically, a little tiny piece
of heat, tries to get across
25 thousand air bubbles, it is
going to have a much more
difficult time of it than if it
tries to traverse the same distance
in open air.

Air bubbles are harder for heat to get
across than open air is, given the same
distance. For example, the distance
between the inner and outer layer of your
ski parka.

Given the same distance, air bubbles are
harder to traverse than open air is. Heat
travels faster and better in open air
than it does when trying to get from the
inside layer to the outside layer of your
parka.

Why? Because on a microscopic level, your
parka is mostly air bubbles. That's why, when
traveling, your ski parka is so easy to squeeze
into your backpack.

You can squeeze your parka into a small
space because the tiny air bubbles deflate
when you stuff your parka into a back
pack.

That, in short, is how most insulators
work.

Most insulators, when fully inflated,
consist mostly of tiny little air bubbles
that slow up, but do not stop, the heat
transfer process.

Ed Abbott