Side airbag device

A side airbag device, comprising:

• an inflator;
• and
• a cushion in a bag shape, the cushion provided at a side of a vehicle seat seatback, the cushion inflatable and deployable with gas supplied from the inflator to a side of an occupant in the vehicle seat,
• wherein the cushion includes:
• a first portion having at least three sides, the first portion including a first chamber that is expandable and deployable;
• a second portion having at least three sides, the second portion adjacent to the first portion, the second portion including a second chamber that is expandable and deployable;
• and
• a third portion having at least three sides, the third portion being non-expanding, and adjacent to both the first portion and the second portion, and
• the cushion in an expanded and deployed state has a columnar or pyramidal shape having a space extending contiguous in the vertical direction that is surrounded by the first portion with the first chamber expanded and deployed, the second portion with the second chamber expanded and deployed, and the non-expanding third portion, the first portion deployable in a forward direction and a lateral direction such that the first portion defines a reactionary surface for further enabling suppressing movement of the occupant seated in the seat,
• wherein the first, second and third portions define a triangle with the first and second portions intersecting to define an acute interior angle.