True down consists of plumules with no quill whatsoever. High fill down has fewer quills than low fill down. Compression does two things to low fill down; it kinks the quills so they provide less loft and it pushes quills through the shell which can result in loss of loft. Anyway, I have gotten much more use out of high-loft down items than low-loft items.

Here are some other considerations:
Oxygen and ozone both attack down, making it brittle and less able to fill space. Cleaning fluids and electrical appliances, among other things, can create ozone. Moths love down, too. So be careful where and how you store down items.

Waterfowl down has natural water repellant oils which is removed by detergents and even mild soap. The safest way to clean a sleeping bag is to wipe the shell with a cloth moistened with rubbing alcohol. I don't ever wash down sleeping bags or quilts.

The safest storage for down bags and quilts is to use them on your bed of as throws. A simple duvet will help keep them clean. They sould never be stored compressed. A loose, large, moth-proof bag is the next best choice after the duvet.