I've always made my quilts with two layers of insulation right on top of each other. However, I've noticed that in most commercially available synthetic bags, they use what they refer to (generally) as a shingled construction, or some other patented variation. The claims I've read on sights say that it creates more air pockets, greater compressibility and greater loft while eliminating cold spots.

Does anyone know how or why shingle construction is really done? Is it truly better than simple layer on layer construction? Or is it a more efficient or easier method of construction for manufacturers?

There may not be all that many "patents" on shingled sleeping bag construction. You can go to http://www.uspto.gov and search the patents for this yourself. The patents are required to divulge the design concept in order to be granted as a patent and receive patent protection.

In general, shingles require more cutting and sewing than do layers. So, there is some more cost, perhaps. The stabalization of the insulation with more sewing could have other disadvantages, such as weight. But, then again, it might not.

At the USPTO site, you may have some problems viewing the illustrations. It seems that so many commercial software firms are so anxious to make their software "your software", you may have browser plug-ins for viewing that are incompatible with the USPTO.

All hail comeptition.