Why is my freezer frosting up? Expert insight on why it happens, and how to fix it

An open freezer drawer full of bags of cut up vegetables.

Too much frost in our freezers is a pain, making it more difficult to grab what's inside while depriving us of precious space inside. For a long time I've wondered why it happens and whether it's avoidable or not.

I caught up with mechanics and appliance experts to find out why freezers frost up, how to fix it and stop it returning.