Does Mylar Make A Difference?

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.

"That's bullshit", I thought.  So I tested it.

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! 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.  

Mylar rescue blanket for wrapping perishable good shipments

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.

Mylar lined box for shipping perishable goods

Here's the packout, bottom to top:

  • Cardboard box, 200# test
  • Mylar rescue blanket
  • 1.5" thick insulation
  • product (We used 7 Paleo Treats) & datalogger
  • 24 oz frozen gel pack
  • bubble wrap
  • approx 1 lb dry ice
  • 1.5" thick insulation
  • Mylar rescue blanket
  • Cardboard box, 200# test

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.)

Testing Mylar lining vs No Mylar on insulated perishable shipping boxesThat graph makes it a little hard to tell how big the difference is, so here are the numbers:

Mylar liner test, by 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.

Mylar wrapped box holds in the sublimated CO2

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.

Rock on!

We are PSYCHED to help you learn how to ship your perishable product across the country.  A consultation with us can save you years of experimenting and thousands of dollars.  Reach out via our Contact form to learn more. 

Here's to your small food biz success!


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Nik Hawks


Nik Hawks helps run the show at Paleo Treats. Fascinated by humans in all their strange glory, Nik is harnessed in and pulling hard in pursuit of excellence with the rest of the PT Crew. Enjoy!

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