It is known that the people who train a sport activity for a long period of time need to drink frequently in order to avoid becoming dehydrated. Since some kinds of activities, such as cycling, keep constantly busy the hands of the sportsman, a knapsack has been devised which internally comprises a container for a beverage. Said container is provided with a thin tube through which the beverage can be sorbed by the sportsman, so that he can drink without having to stop his activity. The knapsack can be thermally insulated by means of fibrous insulators, such as glass wool or rock wool.

However, the insulating features of these materials are not sufficient for maintaining constant the temperature of the beverage for a long period of time.

In order to obviate this problem, it was thought to manufacture the thermal insulation of the knapsack by using thermoinsulating evacuated panels of the known type, for example those formed of a board of open-cells polymeric foam contained in an evacuated envelope.

However, these panels are rigid and can be with difficulty adjusted to the walls of the knapsack that preferably has an anatomical and optionally non-rigid shape, with a higher volume when it is filled of the beverage and a progressively decreasing volume when the beverage is consumed.

Further, since a substantial requirement of said envelope is a high gas- tightness, it is formed of barrier sheets containing aluminum layers which confer to the envelope itself a certain fragility. Therefore, said panels should be placed inside a preferably rigid protective structure in order to avoid the cracking of the envelopes which would compromise the thermal insulation properties of the panels.

Therefore, object of the present invention is providing a thermoinsulating knapsack which is free from the above mentioned drawbacks. Said object is

achieved by means of a thermoinsulating knapsack whose main features are specified in the first claim and other features are specified in the following claims.

The panels used for the thermal insulation of the knapsack according to the present invention employ, as a filling material, a powder of an inert material having average particle size lower than 100 nanometers (nm) and preferably comprised between about 2 and 20 nanometers. It has been found that by the use of these powders, the thermal conductance of the panels varies only slightly, and particularly remains lower than about 8 mW/m-K, for internal pressures up to a few tens of mbar, differently from the panels based on polymeric foams wherein the thermal conductance grows rapidly when the internal pressure is higher than about 1 mbar. For this reason, it is possible to maintain pressures even higher than 10 mbar inside the evacuated panels according to the invention, so that it is not necessary to use envelopes which contain aluminum sheets, necessary above all in the applications at high temperature. This particular measure, which reduces at negligible values the thermal bridge, enables the nearly total utilization of the insulating properties of the filling material of the evacuated panels according to the invention. Due to their very reduced size, the particles of the powders can form, because of cohesive or electrostatic forces, aggregates having size of a few micrometers (lem) or even higher, without causing variations of the thermal insulation properties of the panels.

By using as a filling a block of very fine powder of an inert material, it is possible to obtain evacuated panels which can be bent or curved, so that they can be adapted to the anatomical shape of the knapsack inside which they have to be inserted, as well as to the eventual variations of shape and volume of the container when it is filled or emptied of the beverage.

Further, thanks to their envelope being formed of a plastic multilayer comprising no aluminum layers, the evacuated panels used for the thermoinsulating knapsack according to the present invention are more solid than the known panels based on polymeric foams and can be placed inside the same knapsack without providing a protective structure suitable for preventing the accidental cracking of the envelopes.

According to a particular aspect of the invention, the inert material of the powder is silica preferably mixed with mineral fibers, so that it can be easily compressed in order to make blocks of even a few millimeter thickness, which can be placed in an envelope, evacuated and subsequently curved with relative ease.

Further advantages and features of the knapsack according to the present invention will appear to those which are skilled in the art from the following detailed description of one embodiment thereof with reference to the accompanying drawings, wherein: -Figure 1 shows a perspective view of the complete thermoinsulating knapsack according to said embodiment; and -Figure 2 shows a perspective view of the knapsack of figure 1 from which the external sack has been removed.

With reference to figure 1, there is shown that the knapsack according to said embodiment of the present invention comprises a sack 1 made of a flexible material, for example fabric, provided with two straps 2 for transportation on the back. Inside said sack 1 is positioned a container 3 made of a liquid-tight material, suitable for containing water or another refreshing beverage. Said container is completely closed with the exception of a small upper opening suitable for enabling the coming out of the drink by means of a small tube 4 having the function of a straw. As a matter of fact, one end of said tube 4 is immersed into the beverage inside the container, whereas the other end is inserted between the lips of the sportsman when he wishes to drink.

In the present embodiment the container 3 is formed of an envelope made of a flexible material, for instance plastic sheets, but the use of any other material known for containing alimentary beverages can be involved in other embodiments.

Tube 4 can be fastened at the central portion thereof to one of the straps 2 so that it is always within the reach of the sportsman.

With reference to figure 2, two evacuated, slightly curved panels 5 and 6 are shown to be positioned externally of container 3. Said panels are arranged side by side so that together they form a substantially tubular body whose cavity is

occupied by container 3. Besides, the two evacuated panels 5 and 6 can be fastened to one another by gluing or welding in pairs their lateral flanges.

Evacuated panels 5 and 6 have a thickness comprised for example between 4 and 15 mm and are formed of an envelope of a laminated plastic, optionally metallized, wherein a very fine powder of an inert material is enclosed, particularly silica. The plastic material used for the envelope can be any known material which is considered to be suitable for the construction of evacuated panels of traditional type, for example a polyolefin. The pressure inside the envelope is lower than 50 mbar, whereas the silica powder is preferably mixed with mineral fibers, particularly glass fiber. The silica is preferably pyrogenic silica, a form of silica which is obtained by burning SiC14 with oxygen in a suitable chamber, according to the reaction: SiCl4 + 02- Si02 + 2 Cl2 The silica produced in this reaction is in the form of particles of size comprised between a few nanometers and a few tens of nanometers, which can optionally be agglomerated to form particles of bigger size, as previously described. Pyrogenic silica is produced and sold for instance by the US company CABOT Corp. under the name Nanogel or by the German company Wacker GmbH.

In the present embodiment the internal space of the sack 1 is completely occupied by container 3 and by insulating panels 5 and 6 placed around it, but in other embodiments said sack 1 could be provided with more compartments and lateral pockets so as to serve for the transportation of other objects or food, further to the beverage.

Further variations and/or additions can be made by those which are skilled in the art to the described and illustrated embodiment by remaining within the limits of the invention itself..