In Cumulus down products the brand uses 5 different construction designs for the down feather chambers; each of which is suited to the amount of down used. As for the design of the sleeping bags (and jackets), Cumulus have two principles. Firstly, to be transparent and always keep the customer informed of the construction used in any particular model - which is not the norm with some of the competition. Secondly, they try their very best to ensure that designs and construction methods are more advanced than those of the competition (with a comparable weight of down).
This is the simplest construction design of down chambers. Stitching along the entire length of the insulating surface means there are lines where there is no insulation of down. For this reason this design is often criticised and is not suitable for sophisticated products. It should be noted, however, that the stitching in the sleeping bag does not make you feel as if you were wearing a "ladder" of cold lines. Accordingly this design is perfectly suited for purely summer sleeping bags or light down jackets where it is still widely used.
This is the most common method of construction of down chambers, used by most manufacturers of sleeping bags filled with 200-1200 grams of down. At Cumulus they strive to vary the construction of chambers, depending on the degree of sophistication of the sleeping bag so they only use the H-Chamber in some Spring/Summer models. In “mummy” style sleeping bags filled with 300g of down or more, Cumulus use a more advanced trapezoidal design.
The use of this design in such series such as Lite Line, Panyam and Mysterious Traveller gives the brand an edge over most of the competition which, with a comparable weight of down, generally use more basic solutions - mainly H-Chambers or even stitching. The trapezoid is a more advanced design than the box structure, because there is less likelihood of "cold spots" than with H-Chambers. Trapezoid chamber is used in two and three-season sleeping bags with fillings from 300 to 700 grams of down.
The most advanced design, except for block construction, the V-Chambers afford very little probability of the occurrence of cold spots thanks to the alternating triangular cross section design of the chamber. Cumulus use it in the Alaska 900, Teneqa 700 and Teneqa 850 models. The relatively light weight of the structure has allowed the brand to achieve a level of performance which is difficult to beat on warmth to weight.
The most advanced design in the structure of down chambers, almost completely eliminating the possibility of the formation of "cold spots". Due to the degree of complexity, the use of such a structure makes sense only in the most advanced expedition-sleeping bags for use in the most extreme conditions. In slightly lighter sleeping bags, with the aim of improving the thermal system most cost effectively, it is better to increase the filling than to abandon the use of V-Chamber or Trapezoidal construction methods.