Not possible? It is.
Read on.
Ok, so I love duct tape. Who doesn't? Anyway, I am always needing it and never having it. I mean, a roll of duct tape is impractical to carry around and since I don't have a car to stash it in I end up not carrying it at all.
How do I fix this, I thought to myself. then I remembered what a friend of mine used to do way back when I lived in Colorado. I could flatten it!
Like I said, this is not my original Idea but I didn't see it on Instructables so I thought I'd post it. this should only take you 10 minutes or so plus drying time.

Step 1: What You Need.

What you'll need is:
1 roll of duct tape (it works better if you use a small roll or a half roll.),
A bowl of water,
And somewhere to let it dry.

Step 2: Soak It.

This step is super simple, I don't think you need a picture.
Put the tape in the water.
It's that easy.
Now, let it sit there for a few minutes so the cardboard gets soaked all the way through.

Step 3: Flatten It!

Now, this too is not that hard.
Flatten it.
Wow, that was easy.

Step 4: Just for Fun

And just for kicks I put it in a vice and made it very flat.
Don't squish your fingers now...

Step 5: Use It!

Now you're done.
I keep this in my pocket and use it all the time.
Much easier to carry around now that it's flat. :-P
This was my first instructable, let me know what I can do to make a better one!