For a while now, I've been watching one of our Eureka Factory partners walking around with drinks in doubled up plastic cups, separated by a folded up paper towel. When I inquired, he said it was his DIY insulated cup. If you follow our Instructables group, you may wonder why he wasn't using one of the dozens of drink cozies we found jammed in that drawer.
One, the cozies don't work well with the plastic cups we use and two, we've now repurposed most of our cozies for more important things like shoe inserts and mouse pads. Go figure.
At any rate, while I know the basics of insulation - that air pockets slow heat transfer - I wasn't convinced that the tiny wall with the paper towel air cells between two plastic cups, made any significant difference.
So I decided to test the theory out - and by golly, you were right, honey, it does make a difference!
Step 1: Materials
2 plastic cups
paper towel or napkins
Step 2: Create Paper Divider
Take a single sheet of regular paper towel, or two sections of the easy tear paper towels connected together.
Fold in half,
Then in half again, length-wise.
Step 3: Connect Your Cups
Wrap the folded paper towel around one cup and insert it snugly into a second cup.
Step 4: The Test
To test the double insulating cup idea, I filled three sets of cups half way with similar sized pieces of ice: 1 single cup; 1 set of nested cups with nothing between them; and one set of nested cups with the paper towel divider between them. I put all three outside on the patio for an hour. It was about 85 degrees.
Step 5: The Results: Single Cup
An hour later, the single cup had a lot of condensation on it, and yielded two ounces of melted water.
Step 6: The Results: Double Cup, No Paper
The doubled cups weren't sweating quite as much and yielded just a little less than 2 ounces of water.
Step 7: The Winner! Double Cup With Paper
At the end of the hour, the two cups nested with the paper towel between them had hardly any condensation on the outside, and only about an ounce of water melted from the ice.
Step 8: Picnic Version
So while that's not a Mythbusters level science trial, it does suggest that the double walled cup with the paper towel divider works. But at your garden variety summer picnic you may not have a paper towel roll to pull from. Chances are, though, you'll have some paper napkins.
Just grab a couple of those, open them up, fold them lengthwise and insert between two plastic cups, and there you have it: an Instant DIY Insulated Cup!
Step 9: Pour and Enjoy!
The doubled cups with the paper insulator also slow the transfer of heat from your hand to your drink, so bottoms up! And when people marvel at how your drink still has ice after theirs has melted, tell them "It's Science!"