Down is a natural product and has a higher warmth-to-weight ratio than synthetic insulation and it is also more compressible.
A common down mix is 95/5 mix of down and feathers. The higher share of down the better properties the garment has.
Down garments also comes with different fill power. Fill power is a measure of the loft or “fluffiness” of a down product that is loosely related to the insulating value of the down. The higher the fill power the more air an ounce of the down can trap, and thus the more insulating ability an ounce of the down will have.
When we at Tierra buys down it is certified by RDS (Responsible Down Standard) or bought via our sibling Fjällräven. Here is a video describing the entire down process at Fjällräven: The Down Promise.