Ground Level Seams
Ground Level Side Seams maximise the thermal efficiency of the sleeping bag by allowing a single top-layer to wrap fully around the body. In extreme conditions, with a structurally sound side-wall fewer cold spots can develop. Furthermore by altering the ratio of where the down is held inside the bag, greater control of temperature regulation can be achieved.
Side Level Seams
A simpler method of constructing a sleeping bag; side-level seam bags are typically easier to enter and exit as well as zip-together making them suitable for lighter-weight bags and those designed for less extreme conditions.