If you need boiling water for a mug of hot tea for a walk, a picnic or a hike, we take a thermos. It is also suitable for a portion of food. But if there are a lot of dishes or drinks or you are going on a picnic with a large company, you need a more serious solution. In this material, we find out what thermal bags are, what they are, what they are for and how to choose them correctly.
The principle of operation of the thermal bag
The structure of the thermal bag is quite simple, and its operation is based on thermal insulation. By design, it consists of several layers: outer – dense tarpaulin, nylon, polyester and other durable, moisture-resistant, washable materials; internal – heat-insulating made of foamed polyurethane, foil isolone and so on. Thanks to the inner layer, the bag does not let in or out cold or heat, keeping the temperature in the chamber.
Budget thermal bags keep the temperature only up to 10 hours, which, however, is quite enough to bring food to the picnic area. However, in extreme heat or, conversely, in winter, the temperature regime can be significantly reduced. There are thermal bags with a temperature retention of 24 hours or more, up to 4 days.
According to the principle of operation, all thermal bags are the same. The differences are in capacity and functionality. There are compact bags with a volume of up to 10 liters for several people, there are larger ones – up to 20 liters or more, in the form of backpacks, boxes and even small carts. With pockets, shoulder straps, short handles, molded and padded.
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Cooler bags are different from isothermal ones, although they are similar in appearance. The key difference is the presence of a cooling device. In fact, this is a real micro-refrigerator, which is equipped with a small compressor, runs on isobutane or freon and is connected to the car.
With such a device, you don’t have to worry about the safety of the products at all, but you have to take care of the bag itself. Like any refrigeration equipment, it is very capricious to shaking, vibrations, it cannot be dropped and turned over. In addition, it is completely useless without electricity. Therefore, the cooler bag must be kept permanently connected either to the car or to a separate battery.
Why the bag does not keep the temperature
By itself, an insulated bag does not heat or cool – its task is only to keep the temperature, while it does not completely prevent the loss of heat or cold. It slows down the cooling or heating of food, but heat loss is inevitable.
The main weak point of the thermal bag, as well as the usual thermos, is the loss of temperature upon opening, the so-called air loss. This inevitably happens whenever you need to take something out or put it back in.
The second way of temperature loss is contact, through the materials themselves. Thermoses win in this regard – they are made of glass or steel and have double flasks. Thermal bags aren’t perfect. Foam polyurethane foam copes with this better, but a lot depends on its density.
How to use a thermal bag and extend the temperature
As we found out, even buying a quality branded bag does not 100% protect your products. However, there are several ways to help extend the temperature inside as much as possible.
Proper use of the bag
Try to open the thermal bag less often or not touch it at all if you have a long storage ahead and you need the bag to cope with many hours of work. Some thermal bags have mini valves for quick access – use them, or do not open the bag completely, taking out the necessary items neatly and quickly.
When choosing the thermal bag itself, you should not be guided by the principle “more is better”, an empty bag cools down much faster. Therefore, try to fill the thermal bag completely, leaving as little free space as possible. And do not forget that to maintain cooling, it is worth keeping the bag in the shade and cool, and to keep warm, on the contrary, closer to the radiators or at least not put it on the ground and store it next to other things.
Additional product packaging
The first way is to use additional packaging for products. Wrap food containers, bottles in several tightly tied bags – this way you will make an additional, airy, layer of insulation. An alternative option is to wrap it tightly in food foil. With hot, unpackaged dishes, especially flour, you should be careful – due to steam condensate, the food can become damp.
Put cold accumulators
Of course, this method is not for winter, when food needs to be kept hot. But for a hot summer – just right. The cold accumulator is a sealed plastic box with gel or salt refrigerant. It freezes in a regular freezer and then gradually cools down over 6-12 hours depending on the volume. This is a budget-friendly and fairly easy way to keep food chilled for longer – just put 1-2 batteries in your bag along with your food.
Even cheaper and easier: take an ordinary bottle, pour water into it with a few tablespoons of salt and freeze.
A similar elementary heat accumulator is the same bottle, only with hot water. Remember that boiling water cannot be poured into a plastic bottle.
Choose the right bag design
The design of the bag strongly influences both direct and contact heat loss. To make sure, pay attention to how and from what it is sewn.
It is desirable that at the opening point there is a quick access section and a flap valve, and in the area of \u200b\u200bthe locks – additional fabric pads and sides that hide the zipper. Such details prevent excess air from escaping.
The thickness of the outer and inner materials also affects the temperature retention and the risk of condensation on the outside of the bag. The inside should not be sewn – in general, the fewer seams, the better. Existing seams should ideally be taped to prevent air and moisture loss through micro-punctures from sewing needles.
Bags with several thermal insulation compartments are convenient for separating contents. In one you can put something that you do not plan to take out until the very end, in others what you may need earlier or what you will often take out.
Let’s check how these methods really affect the timing of temperature retention. For the experiment, we took a liter bottle of water at 10°C and put it in a thermal bag for two hours, trying to keep it cold for as long as possible. We compare storage without additional packaging, in a bag and with a cold accumulator.
As you can see, without additional packaging, the water heated up by 5 ° C in just a couple of hours, packaged in two bags was able to save a couple of degrees, and the cold accumulator even cooled the bottle even more.