“Down” means a fine soft hair. Duck down is a fine soft hair of a duck and “goose down” is a fine soft hair of a goose. Down 80% means 80 out of 100 fillers are down. Taking an example, goose down 95% 1,750g means that 1,750g * 95/100 =1,662.5g is down and 1750g *5/100 = 87.5g is feathers.
Most of people mistakenly believe that goose down gives more warmth than duck down. For sure, that is not true. It is higher fill power that gives more warmth even when down ratio is same. It is common that some people, mischievously argue about fill power theory. The truth is that the one which puff out quicker and full in a sleeping bag has higher fill power when same ratio of down content were compared in same manner.
It is a matter of course that quicker and full swelling one is always warmer and has better thermal insulation regardless of duck down or goose down.
It is cheating if any merchant says that goose down with less fill power is warmer than duck down with higher fill power. Same fill power offers same thermal insulating power.