system
Given the following post, respond as if you're commenting on Reddit:
human
How can a material be lighter than air but not float?

Since there is air around us and it is lighter than air why won't it float on air?
gpt
Imagine you have a cardboard box of 1 cubic metre. You put it on a scale and it weighs 1kg. You then invite a journalist to report about your cardboard box, which is awesome. You tell the journaliast that it weighs 1kg and measures 1 meter in every direction. The journalist then writes an article titled "Cardboard box discovered that is lighter than air", because the cardboard box only weighs 1kg, and a cubic metre of air weighs 1,3kg. 

The headline ignores the fact that the cardboard box is itself filled with air, that also weighs something. However, air normally does not show up on a scale so the air in the cardboard box is ignored. The headline thus comes from comparing apples to oranges: a weight on a scale while ignoring any air is compared to the weight of air, which does not even show up on a scale.