Side airbag for vehicle

A side airbag for a vehicle, comprising:

• an airbag cushion disposed between an occupant and a door trim;
• a diffuser disposed at a first side of the airbag cushion, and configured to diffuse gas supplied from an inflator within the airbag cushion;
• a vent aperture disposed at a second side of the airbag cushion, and configured to communicate within an interior of the airbag cushion to an exterior thereof;
• a first seam line spaced apart from the vent aperture by a predetermined distance in a direction toward the diffuser, and formed in a shape that obstructs the vent aperture;
• a second seam line spaced apart from the first seam line by a predetermined distance in a direction toward the diffuser, and formed in a shape that obstructs a second end of the first seam line;
• and
• a third seam line that crosses the airbag cushion in a direction from the diffuser to a position below the vent aperture and separates the airbag cushion into upper and lower portions,
• wherein a seamed portion of the second seam line is separated when a force equal to or greater than a predetermined level is applied to the second seam line such that the gas is vented out by making a detour toward a position below the first seam line after the cushion is inflated, the force being generated by an inflation pressure of the airbag cushion.