I am very curious. I have frequently used a very small summer-rated sleeping bag, but have now bought a somewhat warmer bag, which is less compressible and takes more volume. It will be tested soon. Some sleeping bags in that category used 80 g/m2 polyester fiber as fill, while mine uses 150 g/m2, which is almost 2 times more. Both are similar priced and rated, but mine takes more volume -- it's less compressible and weighs 13 percent more.
Is a more wide, sparse synthetic sleeping bag better, because there is more volume to isolate you from the cold? Or it is the same if you have more dense filling with less volume taken? Is it better to have more dense filling, or to have it more widely distributed with more volume taken for similar weight? What are your experiences?