Tips & Tricks HELP! How do I avoid cotton shrinkage?

Hi.

I've got a bit of a problem:
About eight years ago, before I knew much of anything about dealing with cloth, I made this awesome cloak out of thin cotton. Because I didn't know anything, I made it WAAAAAY too big for what I wanted at the time. But I made it well.

Because the cloak wound up being so big, I didn't wear it at first. Eventually, I realized that it was perfect to wear over some armor that I've been building/rebuilding for almost 20 years.
A photographer took these of me last year:
http://www.flickr.com/photos/jscozzari/2735039930/in/set-72157606556194498/

You can't see them in the pics but it has sleeves that I tucked away, but actually preffer to wear over the arm plates.

Here's the problem:
This cloak has never been washed. No pre-shrinking. Nothing. That's never been a problem. I wear it maybe twice a year.
I just got back from NorWesCon and guess what? It got dirty, and needs to be washed. If it shrinks, it'll be mostly useless to me. But I'm very attatched to the stupid thing and don't want it to become unwearable.

How do I wash it without it shrinking?

My fiance' suggested washing it in cold water and then allowing it to airdry.
Will that actually work?

Please help.

It is the heat that shrinks the cotton, not the detergent or anything. Cold water and airdrying should keep it from shrinking. If you don't have room to place the item outside to dry, hanging it from the shower curtain rod works just as well.

From my personal experience, though, things don't shrink much in the warm water but the dryer is where they like to shrivel up. I'd still use cold water, just in case.

Thankyou-Thankyou-Thankyou!!!

I realize it's only a thing, but it's the first really cool thing that I ever made out of cloth.
And despite being made of thin cotton, it's been so durable. That armor has buckles and pinch points that should have wrecked it by now, but I've never had to do one repair on it.

Again, thank you!

As had been said above, use "cold" or regular tap water (aka no water heater).

When Air-Drying, might also want to allow it to gradually dry up in the shade (but still get some sunlight or warmth of it) thus best not put in direct sunlight. My family Air-dry everything (hey, we got the Sun 12 months straight....well sort off) and I notice that the clothing goes "crispy" and shrink a bit when it's hung in direct sunlight (usually over the balcony railing as our drying area is the balcony so almost everything else get dried in the "shade")

For future projects, pre-shrink the cotton before you sew it.

Well of course I know that NOW, it's just that eight years ago I didn't.

Thank you for the advice everyone.

BTW: I didn't even think of what sunlight could add to shrinkage. Luckily, I washed it too late in the day, so I had to hang it up in the shower with hangars. That was a fun project in itself. I'd forgotten that the bottom hem is almost 12' across!
Oh, and no noticable shrinkage. Before washing, I took measurements of key points (neck, hood, shoulders, arm opennings, bottom hem panels) and everything came out either exact or to within a quarter inch.

Thank you again!