Kamifusen (紙 風 船) Self-inflating paper balloon - Kamifusen meaning paper (kami) balloon (fusen) Kamifusen (紙 風 船) self-inflating paper balloon and it’s a Japanese toy, which means paper balloon. Kamifusen meaning paper (kami) balloon (fusen), is a traditional Japanese toy. You can inflate it by hitting it in the palm of your hand. Despite having a hole being open to air, a paper balloon remains inflated. One might expect that bouncing the paper balloon would force air out of its hole and cause the balloon to deflate. Instead, the hitting it actually increases the paper balloon to inflate, as seen here. Some physicists say the property that causes a crumpled sheet of paper to slowly unfold is similar. This somewhat helps expand the scrunched paper balloon. However, it does not fully explain the inflation, since the unfolding does not completely smooth out plain crumpled paper all the way. Other physicists have suggested that the bouncing cause the pressure changes indie the balloon that alternately push out the and pull in air. That’s ,true, but it is not obvious how the pressure changes and why more air comes in than goes out – a requirement for the balloon to inflate. Part of the genius is the paper from which it is made. The paper is not only lightweight and relatively impermeable to air, but it also has a degree of plasticity that allows it to deform easily and retain its resulting shape. Because of those properties, the balloon inflates to a volume with its air content and maintains that volume until additional air is added. As a result, a squashed balloon can accumulate air and eventually inflate to its full size from repeated bouncing, even though the net pumping from a single bounce may be small. A balloon made of plastic, rubber, or any other material that does not share the key properties of paper would not inflate as the Japanese balloon does. More information in the description on the video

self-infalting paper balloon