I was talking to a buddy at the Farmer's Market who swore up and down that wrapping meat in mylar allowed her to ship 4 days without any thawing.
First, and to be fair, I misunderstood her packout. She uses the same insulation we do AND adds mylar inside the insulation. I thought she was just using Mylar.
She found the idea on Reddit, tried it on a chilly spring week and managed to get a big hunk of meat delivered to a friend in Washington in 4 days without thawing. Pretty good!
But...how does it hold up in the world of shipping small boxes of delicate stuff, like untempered chocolate or coconut oil based desserts?
She gave me a spare mylar foil blanket to test. These ain't fancy, and apparently you can get 'em on Amazon for about $.50 each.
I wouldn't want to use this if I was shipping 30 boxes a day; they're a PITA to unwrap and cut. Still, for testing purposes it was fine, and I was shipping a few boxes where 10 degrees made the difference, this is $.50 well spent.
I lined both the inside and the outside. Here's just the outside lined. I figured if there was any difference that this would show it.
Here's the packout, bottom to top:
And, here I am packing up both boxes at warp speed. :)
I packed two boxes, one with the Mylar on both the inside AND the outside of the insulation, and set 'em up with the dataloggers on a shelf in the back of the office. It was normal summer temps in San Diego, mid to high 70s during the hottest part of the day.
On the graphs & tables below I'm only showing every 4 hours; if you want the full minute-by-minute files reach out via our Contact page and I'll send 'em over.
PT-1 is the box with the Mylar liner (the blue line). PT-2 is the control box (the orange line.)
That graph makes it a little hard to tell how big the difference is, so here are the numbers:
Yep, I was just as surprised as you; there IS something to this Mylar thing; almost a 13 degree difference at the 48 hour mark. Wow!
Now, I know you engineering types are screaming your great egg-shaped heads off about the elephant in the room: Was it the Mylar reflectiveness, or was it the fact that the Mylar made for zero (or low) air exchange?
The effect of the trapped gas was obvious; that Mylar box was bulging by the end.
Maybe that would have changed if we'd knocked the boxes around the way the shipping carriers do; all the bumps might've burped out the gas.
I don't know which it was, so I'll test it. In the meantime, here's one more datapoint for you to make the decision whether or not wrapping with Mylar is right for you.
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Here's to your small food biz success!