Many people resist wearing a bike helmet because once you reach your destination it’s hard to store due to its size, so it’s left hanging on handlebars where it can be stolen and rained on or you just leave it on your desk. Halfdome is a bike helmet that folds in half so you can carry it in a backpack like a book. Two latches on the side of the helmet allow you to detach the top dome, turn it upside down, and drop it into the bottom ring. This reduces the helmet size by half, which solves the storage and carrying problem that many users complain about, helping to reduce the excuse to not wear a helmet. An interlocking edge detail between the two halves of the helmet, combined with the two latches, provides a strong and safe joint between the top dome and bottom ring.