Step 1: Get Some Tyvek
And those are the tent stakes that will be held in the completed sack.
Step 2: Cut and Fold
The two folds will be the sides of the sack--they're not quite parallel, to accomodate the wider tops to the stakes.
Step 3: Glue It
1) Super glue stays slick a lot longer on Tyvek than you might expect. This is because it is activated by moisture, and there's not a lot of moisture on Tyvek--and it doesn't diffuse through quickly (which is what makes Tyvek a useful vapor barrier in construction). Of course, there's plenty of moisture in human skin, so be prepared to peel your fingers apart.
2) Tyvek is already pretty slippery, and until it sets, super glue makes a pretty good lubricant, so pieces can easily slide apart and then glue themselves to something else, such as fingers or desktops.
And of course, a little goes a long way.
Step 4: Put a Stake in It
I'm going to beat this up a bit before I get started on my next Tyvek project. I want to be sure the seams are durable before I put the time, and my remaining Tyvek, into a bike cover.