The Vacuum Insulated Flask was born as a laboratory tool to keep compounds at a stable temperature during experimentation, in an era where refrigeration was still an industrial process.
The domestic refrigerator was a few years away (1913) when the first flasks were produced by the German company Thermos GbmH in 1904 (see Evolution of The Thermos Brand). At the time domestic cooling was achieved by means of an insulated “Ice Box” and the delivery of blocks of ice. This was beyond the means of most households. The ability of the relatively inexpensive “thermos” flask to keep liquids hot OR cold must have seemed like magic, and accounts for the enormous demand for flasks and the early success of the product.
There is a demand for all kinds of insulated bottles and though vacuum insulation is considered the “best”, there are still several insulation technologies competing for different market niche’s. As you will see, not all “insulated” bottles are equal.
These simple and popular bottles are made of glass, plastic, stainless steel or aluminum and are used to contain water or other liquids. Anything hot in them gets cold quickly because of thermal exchange. Anything cold gets warm for the same reason. With hot liquids there is a risk of burning yourself when handling it and with cold, condensation forms on the outside of the bottle. Their main advantage is that they are very cheap to produce and fairly durable.
With plastic bottles however, there are health and environmental concerns. As some plastic bottles age, they give off a potentially harmful compounds called BPA’s. This means that people are more likely to dispose of plastic bottles which end up in landfills and are not bio-degradable. As a result glass and metal bottles are becoming a popular choice, and being reusable and recyclable, are also friendlier to the environment. Active people may prefer aluminum and stainless steel bottles as do not break easily.
Double Wall Bottles
Double wall bottles are manufactured from glass, plastic, stainless steel and aluminum and are primarily for liquids. Here a layer of air trapped between the walls acts as an insulator. This means that heat and cold are retained for a longer period, about 1 hour for hot liquids and 2 hours for cold. Thermal exchange and condensation is still a factor though. Their main advantage is low cost and durability and since these kinds of bottles are made with better quality plastics, the issue of BPA’s does not arise although they are still not bio-degradable.
Double Wall Foam Insulated Bottles
These are the same as double wall bottles but instead of air between the walls there is insulating foam. The best of this kind of bottle use high grade plastics and gain the advantage of light weight, low cost and improved insulation. Hot stays hot for about 3 hours and cold for about 6, and thermal exchange and condensation are no longer issues. These types of flasks or bottles were very popular but are seen less and less as the market is flooded with cheap vacuum insulated flasks of all types.
Double Wall Vacuum Insulated Bottles
At last we get to the “thermos” flask we know and love. They come in all shapes and sizes, and use all the materials mentioned in different combinations. In this design a vacuum is created between the two walls of the bottle or flask (“flasche” being a German word for bottle which entered English in the 14th century) which prevents heat transfer by conduction or convection. These two “bottles” of the vacuum design are not completely insulated as they meet at the neck. The opening at the neck is an obvious place for heat to escape and companies that produce thermos flasks put much of their design effort into caps and lids that reduce thermal exchange at this point.
The original vacuum flask had a double walled glass liner but the most common thermos flasks at the moment are made with stainless steel. Glass flasks are now less popular because they are fragile, but in some applications such as food jars, glass is preferred for health reasons and because it is easier to clean. Well constructed glass and stainless steel bottles both keep liquids hot or cold for up to 24 hours.
Visit the list of the Best Vacuum Insulated Products in each category.