Due to the innate ability of plastic bottles not to be afraid of the fateful blows of fate, it became possible to home conditions to produce shockproof thermos-long-lived.
As shown in the upper image, cut the 2-liter bottle into three parts: the lower, the middle, the smaller and the upper, the smallest. Wrap a bottle with a capacity of 1.5 liters for insulation by alternating with a layer of foil, a layer of foam rubber, and again with a layer of foil, so that the diameter of the “roll” formed does not exceed the inner diameter of the 2-liter bottle. Instead of foam, you can use cotton or other heat insulating material. Insert the finished roll into the bottom of the 2-liter bottle, and put the middle part of the same bottle on top of it. The diameter of the upper hole of the middle part is selected so that it overlaps the lower one and at the same time tightly fixes all the insides of the thermos.
If, as a result of your labors, you get something similar to the one shown in the figure a little higher, you can safely put this in your pocket and assume that you have a long-lived thermos in your pocket.