thermal blanket heat radiation

[Billy The Impale]

So imagine I'm on a cot and I've got a fire in front of me. Maybe I've got a space blanket behind the fire reflecting heat my way, and maybe I've got one behind me. But in addition to those, what if I put one underneath me, so it's facing the fire absorbing the heat? Would the heat it absorbs transfer to my body? Does it work that way?

[Happy Joe]

Re: thermal blanket heat radiation

...'fraid not; solar blankets are fair to good heat reflectors but not particularly good (actually poor) at insulation or absorption & re-radiation.
What I have found works well is a good sleeping bag with additional insulation between the bag and the ground or between the bag and the cot. For cold weather I prefer a lightly ventilated tent. Many; especially cheap, tents have so much ventilation that they provide essentially no shelter from the cold wind/breeze.
In some areas it is illegal to leave a fire unattended (by not staying awake and tending it; because of the danger of forest fire)... the ticket and fine can be substantial...
IMO, its best to put the fire out each evening before you crash then get a good warm nights sleep in the bag, on the thick foam pad, on the cot in the tent without worrying about burning down the forest (and yourself).

Enjoy!

[MacGyver]

Re: thermal blanket heat radiation

Like HJ pretty much said, the Mylar blankets don't act as mirrors for heat, reflecting heat from any distance. For keeping warm, they work best when kept as close to the body as possible with as few openings as possible. It's almost a myth that they're some super fabric that will keep you toasty warm when, in reality, they're survival gear. That means they'll hopefully keep you from freezing to death but not really comfortable. I actually use them for the opposite reason - to keep things cool. I keep the sun off my cooler with one and take naps under one in my canoe when the sun breaks over the trees when the sun gets too hot to fish.

[a65hoosier]

Re: thermal blanket heat radiation

Like HJ pretty much said, the Mylar blankets don't act as mirrors for heat. For keeping warm, they work best when kept as close to the body as possible with as few openings as possible. It's almost a myth that they're some super fabric that will keep you toasty warm when, in reality, they're survival gear. That means they'll hopefully keep you from freezing to death but not really comfortable. I actually use them for the opposite reason - to keep things cool. I keep the sun off my cooler with one and take naps under one in my canoe when the sun breaks over the trees when the sun gets too hot to fish.

MacG - I think you meant not an insulator, or ability to absorb/release heat. The mylar's do a decent job of being a reflector/mirror of heat as your summer usage shows. But it has to be fairly close in also in winter to get some benefits...

Some examples: Many bushcraft shelters also will utilize one on the back wall to reflect campfire heat (and provide some wind break). I've got a couple of dehydrated meal cozies made of reflective materials (however, they're also insulated) that will keep a meal hot for a long time. Many pads (Therm-a-Rest Xtherm and the hard cell Zlite Sol come to mind, use a reflective layer inside or outside to reflect the sleepers heat back to them along with some good dead air space design (these pads also are very lightweight as they skip the synthetic or down insulation and use baffles/reflective materials inside while still providing good R values).

Agree on mylar blankets being not very comfortable wrapped up tight due to condensation and lack of breathability (and zero insulation-but will provide windbreak)...but if that's all you've got...and you need it, then you utilize it accordingly. I have one...but it would be a last resort for me and it means I've been caught unprepared and failed my Plan A, B, C, D.....etc. lol.

Billy - as others have indicated....nope, it won't absorb or radiate fire heat back to you later sitting on the ground. It will however keep your boots clean and dry as you sit in front of the fire...that's about it. What do you have to insulate you from the cold air under the cot as you are sleeping and the fire dies down? Without something (pad/blanket/etc between you and the cold air under the cot...you're probably gonna be cold---depending on temps---and up stoking the fire every couple of hours isn't a restful sleep). Don't count on just fire or mylar to provide your warmth at night. Mylar is fine in an emergency/pinch...fire is great, but each night generally has a "brrrrr, I'm cold awakening moment" which indicates it's time to tend to the fire. You need to think insulation. Insulation (your "sleep system") should be your first step for overall safety/reliability/comfort. Over time, you'll be able to dial in your gear for your comfort level at certain expected temps.

[MacGyver]

Re: thermal blanket heat radiation

MacG - I think you meant not an insulator, or ability to absorb/release heat.

You're right. I edited that post twice and still thought something was wrong with it. Lesson learned: Resist the temptation to get technical with a lack of sleep while on pain pills. ON WITH THE SHOW!