Locking liner for helmet

1. A helmet comprising:

an outer shell comprising an outer surface and an inner surface opposite the outer surface, wherein the inner surface of the outer shell comprises a locking mechanism that is part of the outer shell and extends from a top of the inner surface of the outer shell, wherein the locking mechanism comprises:

a vertical portion that extends away from the inner surface of the outer shell to a distal end, and

a horizontal portion that extends from the distal end of the vertical portion to form a gap; and

a locking liner disposed within the outer shell, the locking liner comprising a locking piece comprising a threaded lip that is sized to mateably couple with the gap of the locking mechanism of the outer shell, wherein the gap is sized to receive the threaded lip of the locking piece, to releasably couple the locking liner to the outer shell.

2. The helmet of claim 1 , wherein the locking liner is releasably coupled to the outer shell with a mechanical connection of the locking piece and the locking mechanism of the outer shell without hook and loop fasteners and without an adhesive.

3. The helmet of claim 2 , wherein the locking piece comprises a circular footprint to allow the locking piece to rotatably engage with the locking mechanism of the outer shell.

4. The helmet of claim 1 , wherein the locking liner and the locking piece comprise expanded polypropylene (EPP), expanded polystyrene (EPS), expanded polyurethane (EPU), or expanded polyolefin (EPO).

5. The helmet of claim 1 , wherein:

the locking liner comprises at least one side piece and a top piece;

the at least one side piece comprises a first lip along an upper edge of the at least one side piece;

the top piece comprises a second lip disposed at a lower edge of the top piece and a third lip disposed around a central opening of the top piece, the second lip sized to mateably couple with the first lip of the at least one side piece; and

the locking piece comprises a fourth lip around an edge of the locking piece, the fourth lip sized to mateably couple with the third lip of the top piece and releasably couple the top piece and the at least one side piece to the outer shell.

6. The helmet of claim 1 , wherein an adhesive or hook and loop fasteners are disposed between a portion of the locking liner and the inner surface of the outer shell to releasably couple the locking liner to the outer shell together with a mechanical connection of the locking piece and the locking mechanism of the outer shell.