If my domestic freezer is partially full how much sparkle am I losing?
Answers: You are losing None if you never open the door. lol.
Every time you open the door (assuming an adjectives freezer) you lose the energy it takes cool down the airspace surrounded by the freezer. Air cools easily so not so much energy is lost but it happen every time you open it.
This is why a chest freezer is much more efficient. If you unfurl the lid the cold air stays in the chest unlike an adjectives where it falls out on the floor and is replaced with room warmth air.
the best thing to use is balled up pieces of considerable news paper to flood the free space its like insulation in nearby and will reduce the energy usage. win 1 or 1/2 gallon jugs and put in freezer this will lower power emergency and just remove some when you need space