High Sierra Topix

I have an older Northface "Kiln" sleeping bag that's rated to 20 degrees. It has a polargaurd filling and must weigh at least 3 lbs. I just bought another Northface bag, the "Orion" that's also rated to 20 degrees (on sale at REI). It weighs in at 2 lb 6 oz and is primaloft filled.
The older bag is thicker (loftier ?) and heavier, yet both are rated at 20 degrees. Can this be ? Does anyone know how those ratings are made ?

I do not believe there is a universal standard used by multiple companies to rate their bags - it should be based upon loft height, but I've inquired to many companies in the past about loft height (including north face and REI) and they didn't have a clue what I was talking about - it was based on fill weight. But I believe in the case of synthetic bags, it is based upon what synthetic insulation is used and the weight of the insulation used because synthetic insulation can very in their warmth/weight/loft ratio. I've read in the past that primaloft is supposed to have a better warmth to weight ratio that polarguard, approaching that of down in warmth to weight, which may be why your polarguard bag is heavier. Western Mountaineering and feathered friends - two highly respected down bag makers - base their ratings upon loft and comparing their ratings/loft shows they are very similar.

Thanks, trailblazer. That's exactly what I was looking for.