The nominal volume of a thermos is the maximum amount of contents that it can be guaranteed to contain.
This parameter is directly related to the type (see above). So, a capacity
of up to 500 mL is quite normal for a thermo mug, a flask or a baby thermos, but it is considered small for a classic thermos, and even more so a jug or a thermos for food. The
"500 to 1000 mL" category includes most traditional and food models; for mugs, flasks and children's thermoses, this is actually the maximum volume. Among the jugs there are many more capacious options —
from 1000 to 1500 mL. A volume
of 1500 to 2000 mL is considered quite large, and the most solid models can hold
more than 2 liters.
Anyway, a large volume allows you to hold more drink or food, but the downside of this is an increase in the size, weight and price of the thermos itself. Therefore, when choosing, you should not chase the maximum capacity, but proceed from real needs. For example, a model of 400 – 500 mL is quite enough for two cups of coffee, and for tea drinking at a halt for 3 – 4 people, it is advisable to have a model of at least 1000 mL. More detailed selection recommendations can be found in special sources; especially they will be useful to those who choose a thermos for long-distance hiking trips.
The type of main cover provided in a thermos. The main cover in this case is a device that directly covers the working volume of the vessel; an additional cap can be installed on top of it, which often also plays the role of a cup. In modern thermoses there are the following types of main lids:
screw-on (screw),
valve,
cover,
hinged cover,
drinking cover,
pump (pump),
stopper. Here are the features of each of them.
- Screws on (screw). Solid (without holes) screw-on cover, secured with a thread. Such lids are very simple and at the same time reliable, but you cannot drink or drain the contents through the classic screw - you have to remove it completely. There is also a more advanced design that allows you to drain the contents without removing the screw - just partially unscrew it; however, this is a rather specific option that is not used often. Be that as it may, twists are found mainly among classic and food thermoses (see “Type”), for which the mentioned nuances are not decisive.
- Valve. A cover (most often threaded) equipped with a valve through which the liquid contents of the thermos can freely flow. Such lids are more complex and more expensive than “blind” screws (see above), but to access the contents you d
...on’t need to unscrew the screw every time, just open the valve. This not only provides additional convenience, but also reduces heat loss. Thanks to these advantages, valves are extremely popular in classic thermos flasks; they are also often used in thermal mugs (see “Type”). The disadvantages of this option include the fact that the valve opening is usually made quite narrow and is easily clogged with impurities (for example, tea leaves or coffee grounds). Therefore, the valve can only be used for liquids without such impurities (this also applies to food thermoses, which can also be equipped with valves). However, there are models with two different valves included, for drinks of different consistencies and aromas.
- Lid. Lids in this case are devices that do not have threads (unlike the screws described above) and are held in place solely by friction or a latch. The design of the lids can be different: some cover the neck from the outside, others are pressed inward when closing; There are also more specific options. In any case, the lids are easy to remove and put back on, but they are not very reliable - for example, it is not recommended to turn such vessels over. Therefore, this option is found mainly in thermal mugs and thermoses for food (see “Type”), for which the mentioned disadvantages are not critical.
— Hinged cover. A variation of the lids described above, which, when opened, is not removed entirely, but is folded to the side on a special mount. Thanks to this, the likelihood of loss is reduced: in fact, you can only lose the cover along with the thermos itself; and a latch, spring, or other similar device is usually provided to hold the cover in the open position. On the other hand, mount somewhat affects the price and dimensions of the vessel. This drawback is least critical for flasks and mugs (see “Type”), and it is among these types that hinged lids are most often found.
— Cover-drinker. Lid (regular or threaded), complemented by a special hole for drinking. This design allows you to drink from the vessel without removing the cover; and during “non-working” hours the hole is covered with a flap or other similar device. Drinking lids are extremely popular in thermal mugs and auto mugs (see “Type”): they allow you to drink from the mug comfortably while at the same time minimizing heat loss and the likelihood of spilling the contents.
— Pump (pump). Lid (classic or threaded) with built-in pump. Most often, this pump is activated by a special button: when you press this button, a portion of liquid comes out of the spout, and the thermos does not need to be tilted. However, such devices are quite complex and cumbersome, so it makes sense to use them only in thermos jugs (see “Type”): the size and weight of the pump is small compared to the dimensions of the jug itself, and tilting such a thermos can be difficult - it’s easier to use a pump.
- Cork. A classic stopper that fits tightly into the neck of a thermos and is held in it without threads or other similar devices. Corks differ from the lids described above in their greater thickness, and also in that they are inserted into the neck from the inside (while the cover can cover the vessel from the outside). Plugs are very easy to use, but have low reliability, which decreases even more as they wear out. As a result, this option has practically fallen out of use.
