Oooo OUCH! I MUCH prefer my method :-), but I expect yours would work...... Anger is also an emotion that raises the temp, and pain likely will also.....:-)

gimpy

Hot rocks under the sleeping bag work well, but the method requires advance preparation. A shallow 6x3 foot trench is dug and the hot rocks are buried a couple of inches down, and covered with dirt and bedding.

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400F seems way too high. I worked in plastics for over 20 years and the glass reinforced nylon polymers we used in structural foam molding were molded in the 500F-600F range. I would not advise putting anythnig like a hot rock inside a synthetic sleeping bag. Boil some water, put it in a Nalgene bottle and wrap it in socks or towels. I can assure you a melted sleeping bag will sleep much colder than an intact one.
YMMV

BTDT.

Camping in the open on the coldest night of the year with a substandard sleeping bag. Sat by the fire all night drinking tea and tucking hot rocks down by my feet. I put them in a canvas bag, but still managed to scorch a few holes in it.

It works, but its hard to tell the difference between hot enought and too hot, especially when numb with cold. I agree that a hot water bottle is probably safer.

i have tried the hot rock trick a couple times by just moving one from the fire to the tent vestibule with a heavy wire cooking grate.i let it warm up the tent,a Timberline,and get some of the damp out of it but even sitting off the dirt on a couple other warm rocks that i could move with leather gloves it went cold within 20 minutes and it was red hot when i moved it.i think this is a overrated camping trick.you would need a big fire and lots of good size rocks to get any effect.the old camping books show a guy sleeping away over nice warm rocks that are buried in the ground under him.ever try and dig a trench at a campsite?.unless you were at a beach it would take hours,and then more to collect the wood and rocks.i have put a candle lamp in a tent to do the same thing with good results and thats why i carry the weight of a small Gaz lamp,with one of those you have a hot tent in minutes.your water bottle filled with hot water in a sox works fine.the problem with the hot rock and other camping "tricks" is that people think they will be able to depend on them if need be and cut back on real gear,and in the end are cold and unhappy..if they survive

These are good techniques to know, but nothing beats an adequate sleeping bag.