Weird Trick To Stay Warm Down To -10 in a t-shirt


With hunting season and fall hiking upon us and winter around the corner, I wanted to give you a couple of extremely compact winter survival tools that will help you maintain core temperature in the most extreme conditions.  If you live in a more temperate climate, keep in mind the fact that most cases of hypothermia happen when the temperature is in the 50s.  Why?  It’s the perfect temperature that encourages activity, sweat, lighter than necessary clothing, and big temperature shifts due to the sun.  In other words, this is something you need to know regardless of whether you live in Alaska or Hawaii.

In the picture below, I show a shelter system I use that has worked very well for me.  I would not suggest trying this, but I’ve used it down to -10 with only pants and a T-shirt on.

Display Images To See The Picture

Figure 1 – Left: Flexible Mylar Bivvy; Middle: Bag Liner; Right: GI Poncho;

On the left we have the flexible mylar bivvy.  It is a thin flexible plastic “sleeping bag” that’s lined with mylar to reflect heat.  There are a couple of different brands of these, and >The Tact Bivvy 2.0< is my current favorite.  The packaging is smaller than any other mylar bivvy I’ve tried, but it still packs all of the great features. Both my 7 year old and I can comfortably fit into it at the same time without stretching, ripping or tearing the bag.  It’s worth getting one for each car you own.  In addition, I carry one in my running/hiking/hunting pack that I use this time of year.

Many 72 hour kits come with Mylar bags, but Mylar tends to crinkle and tear.  I oftentimes wonder how many people selling 72 hour kits with traditional mylar blankets have actually spent a night outside using one to keep warm.  Over the years, I’ve gone from being mildly annoyed with these cheap sheets of mylar to *almost* getting to the point where I think it’s criminal negligence to include them in entry level kits.  Why?

Normal mylar emergency blankets, in a word, “suck.”  Of those who have actually used them and made it through the night using one, I wonder how many had a blanket that was still holding together enough to use for a second night.  If you doubt my assessment of traditional mylar, pull out one of your mylar blankets/bags and see how it performs.  SOME are good…most are not.

And if you really want to test it, let it ride around in a backpack or in your car for a few months and see how well it holds up.  I would bet you that if you’ve got a traditional thin mylar blanket for more than a year and try to use it, it will fail immediately at the fold edges or corners.

Plain thin mylar sheets ARE functional, WAY better than nothing, and provide more heat retention per ounce/dollar than almost anything else you can buy, but they do have serious shortcomings.  If you know them and are comfortable with them, you won’t be disappointed by them in a survival situation, but if you naively expect them to be more than they are, you’ll be disappointed.

The TactBivvy 2.0 that I use is flexible, doesn’t tear, costs less than $20 and they still reflect about the same amount of heat as Mylar. They are great tools.  In addition, they’re a lot quieter than Mylar.  If you’re a light sleeper, like I am, this makes a huge difference in your quality of sleep.

The middle bag in the picture is a Sea To Summit / Thermolite bag liner. A bag liner like this one will add 10 or 20 more degrees of temperature rating to your sleeping bag, regardless of whether it’s a bivvy or a full fledged sleeping bag. These will allow you to use the same 30 or 40-degree sleeping bag year round by letting you simply add a liner for three and four season camping.  The one I use (+15 degree bag liner) adds 15 degrees to ANY sleeping bag.  They also make a +25 degree bag liner.

A big reason to use bag liners is that if you’ve ever backpacked for a week or two, your bag can get to smelling pretty funky. A bag liner allows you to take the bag liner out and rinse it off in a stream every day, giving you a much-much cleaner smelling sleeping bag.

When combined with the SOL bivvy, it gives you a little more insulation and warmth in a small, lightweight package.

Another practical use for these is to carry them while traveling to avoid bed bugs in hotels.

In any case, what I do is use the bag liner close to my body, and the bivvy outside of that, and the reason I do that is for flexibility. On a very warm evening I can just use the bag liner or nothing at all, but I like the bag liner because it gives some instant protection, and if it is colder, I can use just the bivvy or a combination of the two.

I’ve used this combination successfully down to -10 degrees, outside, on the ground, with no supplemental heat or cover.  This is really something you want to avoid.

If you start out cold or can’t get warm, this setup has the added benefit of reflecting the majority of the heat put out by chemical hand and body warming packets.

One thing that you’ll learn, and you’ll learn it faster the colder it is, is that you’ll lose a lot, if not most of your heat to the ground in this setup.  To combat this, you want to insulate yourself from the ground.  If you don’t have a camp pad, pile at least 6 inches of leaves, pine needles, or other debris that is “cushy” and traps plenty of air.

In a rain situation, it’s hard to beat a GI Poncho like the one shown on the right (photo), and specifically a poncho with grommets on the corners so you can make it into a tent. The “tent” doesn’t have a bottom, it doesn’t have walls.  All it has is an A-frame roof, but with the combination of these three items you can have shelter in most situations.

But if you only get one, get a couple of the TactBivvy 2.0s.  The latest generation is smaller than any other flexible mylar bivvy I’ve tried and you can’t go wrong with them.

Please follow and share:
Pin Share


  • Kevin

    Reply Reply October 5, 2018

    I have the same set-up that I take with me on every emergency deployment (I also take the poncho liner)……I’ve found that it gives me the most flexibility from “hot to cold”…….great article!

  • Don Heater

    Reply Reply October 10, 2017

    Why not just put a poncho together with the liner and have a little protection from damp weather too.

    • Ox

      Reply Reply October 12, 2017

      You can! That’s why I showed and talked about a GI poncho. The reason I’m so gung-ho on the TactBivvy is because it’s smaller than my fist, gives me protection from damp weather, and has kept me warm in nasty conditions.

  • left coast chuck

    Reply Reply October 10, 2017

    I keep several of those cheap mylar bags in my car. Not for me, but in case I come across someone who needs something to keep warm. My daughter happened upon an a car that had just overturned. The woman driver was laying in the dirt. It was snowing and was quite chilly. Of course, the woman didn’t have on any warm winter clothes. My daughter took off her brand new ski jacket that she had just purchased for the trip and covered the woman.

    When the EMTs arrived, they loaded the woman with my daughter’s jacket into the ambulance. My daughter tried to retrieve her brand new ski jacket but was turned away by the EMTs. It had never occurred to her that scum sucking lowlifes stop at emergency scenes to see what they can steal and the EMTs, knowing this do not allow anyone to remove property from the scene. Lesson learned. I

    f you are lying by the side of the road you are not getting my new $500 leather jacket from Beretta, you are getting the $1.95 mylar bag. If you are in an especially bad way, you might even get two mylar bags but you still ain’t getting my new Beretta leather field coat that I have been saving up for the past five years.

    In addition, should I somehow leave my rain gear at home and have to change a tire in a downpour, the mylar bag will sort of keep me dry while I am messing with the tire and will stand out so that drivers can see me while I am crouched down by the side of the car. If you are wearing a camo poncho and it is raining and dark — well, one of the reasons for camo is so that people can’t see you easily. If it gets greasy or gets torn, well, no big loss.

    • Ox

      Reply Reply October 10, 2017

      Good stuff, Chuck!

  • Nathan Koets

    Reply Reply November 8, 2016

    Great reading. Reminded me of my first backpacking trip in the early 1990’s. Northern Michigan, on N.Manitou Island. Offloading our gear hand to hand, from the boat and down a gangplank, someone dropped my Kelty sleeping bag into the drink, and in true rookie fashion, I had neglected to drybag it. Soaked, and it was cold and nearly dark. Fortunately, although I had been teased about it, I pulled out the Mylar blanket. Yes, it sucked in the noise department, but that thing saved my butt. I actually had to throw it off several times, or I would’ve roasted, lol. My friends still tease me for over-packing and prepping, but they no longer consider the Mylar “dead weight”… the six D-cell MagLight I brought with me on that same trip? Now that’s another story – I’m never gonna live that one down. ?

  • Mark

    Reply Reply October 23, 2016

    More a question than comment.
    I’ve read reviews on survival bivvy products, and one of the main concerns is breath-ability. Will this bivvy allow sweat to evaporate or will you swelter inside it?

    • Ox

      Reply Reply October 23, 2016

      They don’t breathe. Keep in mind that if the temperature is such that you would swelter inside of it, it may not be the right tool for the job. You can always use it as a blanket instead of a bivvy or only pull it up to your belly or mid chest and keep it open instead of closed off.

      The nature of “survival” is normally such that you don’t have ideal conditions or gear. If you did, it would be camping and not survival. This is an awesome tool that I have used both in the backcountry as a bivvy AND in more controlled situations. A lot of times, when I’m working outside in and out of our quad for extended periods, I’ll simply stick one or both of my sons in the TactBivvy in the passenger seat in their winter clothes. They can cover or uncover themselves as needed to self-regulate temperature and they work great as a light weight, inexpensive, waterproof, cold weather survival tool.

  • Mark Bozek

    Reply Reply October 21, 2016

    Great article. My unit had occasion to be
    in Gitmo and because we would only be there
    a couple days and it was after all Cuba a lot
    of the guys neglected to bring their sleeping
    pads and slept on nylon cots in sleeping bags.
    They were miserable. The night air convected
    through the bags (elevated above the ground
    resting on the cot) and sleep was almost
    impossible. By all means insulate your gear.
    Could prevent a lousy night sleep or worse…

Leave A Response

* Denotes Required Field