Hi! Great question.
Porcupine quills are like big, very stiff hairs. They are made of the same stuff as our hair and fingernails. The quills are sharp so other animals stay away and the porcupine stays safe.
- Sharp and protective: If something tries to bite or touch a porcupine, the quills can come out a little and stick into the other animal. That hurts the other animal, so it usually leaves the porcupine alone.
- They don’t shoot out: Quills don’t fly out like arrows. They only come out when something touches them.
- Not for swimming: Some porcupines can swim, but the quills are not filled with air and do not make the porcupine float like a balloon. Quills help protect, not float.
- Baby porcupines have soft quills when they are born. The quills get hard soon after, so the babies learn to be safe too.
So your idea that quills keep a porcupine safe is right — but they aren’t filled with air and they don’t really help the porcupine swim.