This invention concerns improvements in and relating to sleeping bags, especially sleeping bags for use in extreme weather conditions, where body heat retention is vital.
Sleeping bags generally comprise two layers of fabric with insulating material sandwiched in between. Sleeping bags for use in extreme weather conditions are usually shaped to fit more closely to a user's body, e.g. are narrower at the feet end and wider at the shoulders end. In addition, long lengths of zip fasteners are avoided compared to conventional sleeping bags, as these are areas through which heat can be lost.
US Patent No. 3,831,206 discloses a sleeping bag with a top part and a bottom part, wherein the top part slightly overlaps the bottom part of the sleeping bag, and the top part has a thicker layer of insulation than the bottom part of the sleeping bag.
For sleeping bags usable in extreme weather conditions, there are two main requirements. The first is that areas through which heat loss can occur need to be at a minimum and the second requirement is that the weight of the sleeping bag should be kept as low as possible without adversely affecting the heat loss requirement.
A first object of the invention is to provide a sleeping bag capable of meeting the above-mentioned first requirement.
A second object of the invention is to provide a sleeping bag capable of meeting the above-mentioned second requirement.
According to this invention there is provided a sleeping bag having an inner layer and an outer layer with one or more layers of insulation material therebetween, forming top and bottom parts, the thickness of insulation material in the top part being greater than the thickness of insulation material in the bottom part, and the top part extending around a greater portion of the perimeter of the cross section of the bag than the bottom part whereby edges of the top part extend partially under a user's body, in use, the sleeping bag being characterized by additional insulating material being provided in at least one of the areas intended to surround a user's feet, chest or head.
By having the top part extending effectively partially underneath the user of the bag, there is created a wrap-around effect that helps to keep the user's body warm. By having a thinner layer of insulating material in the bottom part than in the top part, the weight of the bag may be kept down.
The preferred sleeping bag of the invention is shaped to fit a user's body, typically by being narrower at the feet and wider at the shoulders.
It is further preferable that two layers of insulation material be provided in the top part of the sleeping bag with three layers in the feet, chest and head areas of the bag.
This invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: -
Referring to the accompanying drawings, a sleeping bag 10 is shown designed for extreme conditions i.e. for experienced campers, mountaineers and expedition members. The sleeping bag 10 is shaped to fit closely to the body shape i.e. is narrower at the feet and wider at the shoulders. The bag 10 generally has an inner layer 12 and an outer layer 14, between which are one or more layers of insulating material 16.
The sleeping bag 10 has a top part 18 and a bottom part 20. The top part 18 is sized and arranged to cover a greater area than the bottom part. In other words the top part 18 extends around the bag so that its edges will extend partially under a user's body. This creates a wrap-around effect on the top layer to reduce potential heat loss, hence keeping the user's body warmer.
The thickness of insulating material in the bottom part is less than that provided in the top part. That is done in order to keep the weight of the bag down.
In areas of the bag surrounding a user's feet, chest and head (22, 23 and 24 respectively), extra thickness of insulation material is provided. These areas are where most heat loss occurs, so that chances of keeping warm in very severe weather conditions are improved.