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SESK: Stuff Everyone Should Know · sesk.info/scuba-balloon-half-volume

A balloon filled at the surface is carried down to 33 feet. What happens to its size?

It shrinks to half its surface volume.

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  1. It stays the same size
  2. It doubles in size
  3. It shrinks to half its size ✔

Why: Pressure doubles at 33 feet, so the air inside is squeezed into half the space. Bring it back up and it grows to full size again.

Huh, didn't know that: The same squeeze happens to your mask, ears and wetsuit bubbles, which is why wetsuits lose warmth and buoyancy at depth.

The dad joke
That balloon got so deep it lost half its personality.
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References

Answer: It shrinks to half its size. Pressure doubles at 33 feet, so the air inside is squeezed into half the space. Bring it back up and it grows to full size again.

  1. PADI: Diving Physics blog.padi.com/diving-physics
    Reduces to 1/2 that of at the surface
    Checked 2026-10-12.

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