It is quite difficult and not cheap to buy a good thermos. The proposed industrial versions of thermoses are not always convenient, so sometimes you have to improvise, making a thermos with your own hands. Especially since there is an alternative to the industrial product, and it is quite easy to make a good thermos with your own hands.
How to choose a thermos:
Walking around the bazaar, in search of a thermos, you should pay attention to the integrity of the body and the quality of the material from which the cap is made. Rubber and plastic in the lid of the thermos play a significant role, they should be non-toxic, and safe for the human body. Thermos, like any container for water, should be closed hermetically, and on the principle of action, the thermos is arranged as well as a Dewar vessel – full thermal insulation. To find out whether the thermos is of high quality or not, you can only dial there boiling water (well, or cold water). Pour boiling water, screw the cork, wait a couple minutes and touch the thermos with your hand, if it is warm – safely throw away, as it means that the thermos junk! The best variant of the thermos is the one made of vacuum-minimized glass. But it is also extremely difficult to get it nowadays at a similar price.
How to make your own thermos:
The principle of a thermos is thermal insulation. It is very simple, inside the thermos case there should be a vacuum (no molecules – no heat transfer), but it is not always realistic to achieve vacuum at home. Therefore, heat must be insulated by other methods.
The most affordable material is Styrofoam, it is everywhere in bulk, and you can just buy it at the nearest construction store. I did it like this:
I had a piece of polystyrene foam and a Chinese iron thermos – it worked at first, but then something went wrong… And since it is dear to me as a memory, or more precisely to say to buy a new one, I decided to insulate it. I took polystyrene foam (they insulate houses with it), although, pressed foam plastic is also suitable, and began to cut out of it rings, according to the size of the thermos body.
Monotonically, carefully, using a sharp kitchen knife, slice the rings and thread them onto your thermos.
Also, you can use glass containers (juice or mineral water containers with iron lids are suitable).
I then tried this with a glass mineral water bottle, and everything worked quite well. The thicker the foam layer, the better the thermal insulation.
There is one more subtlety here, in order to keep the Styrofoam from crumbling, and for more or less strength of the construction, I recommend stuffing it all into a cut plastic bottle.
The main thing here is to put it there tighter, the tighter the insulation, the better for heat preservation. The plastic bottle acts as a holding frame. I also recommend to hold the whole construction over the fire, as the plastic bottle has good shrinking properties, it will tighten the polystyrene foam, but do not allow ignition!
Well, this is how the thermos became a thermos again. Although it should be noted that heat losses continued through the lid, it also needs to be insulated, and so. thermos with your own hands can be made quite quickly and easily.
