The working volume of the bottle is the amount of liquid for which it is designed. If you fill it “under the cork”, a little more drink can fit inside, but this is still undesirable.
The volume is selected by the manufacturer, taking into account the age the product is designed for and what type it belongs to (see above). So, for newborns, 100 – 200 mL is most often enough, in the category "from 6 months" there are already models for
300 – 400 mL, and for older children (from 3 years old) drinkers of
500 mL or more are produced, similar to flasks of "sports » appointments for adults. All these values are quite justified from the point of view of science. So when choosing, you should focus mainly on the “age category” and type of bottle, and only then — on its volume; especially since models of the same class and in terms of capacity do not differ much.
