Air bag having a high burst strength

A beltless air bag with a high burst strength comprising a circular bottom cloth and a circular top cloth each formed from a woven fabric piece, having warp yarns and weft yarns superposed on each other and seam-joined to each other at a circumferential edge portion thereof, the circular bottom cloth having an inflation connecting hole formed in a center portion thereof through which an inflator can be connected to the air bag and having a circumferential portion thereof surrounding the inflator-connecting hole reinforced with an apron having an inflator-connecting hole, said apron being made from a woven fabric piece seam-joined to the bottom cloth by circumferential seam lines wherein an outermost circumferential seam line on the apron is in a quadrilateral form selected from substantially regular square, rhombic and rectangular forms, said quadrilateral form having vertexes and having the same center point as that of the inflator-connecting hole;

• the outermost circumferential seam line having a pair of sides extending in parallel to each other and substantially parallel to the direction of the warp yarns or the weft yarns in the bottom cloth and satisfying the requirements that:
• (1) when an imaginary circle having a diameter Dw is drawn around the same center point as that of the inflator-connecting hole on the apron in such a manner that at least one pair of vertexes of the outermost circumferential seam line, spaced at a largest diagonal distance from each other, is inscribed in the imaginary circle, a ratio of each of straight line distances Da and Db between one of the vertexes inscribed in the imaginary circle and each of two vertexes adjacent to said one of the vertexes to the diameter Dw of the imaginary circle is in a range of from 0.6:1 to 0.9:1;
• and
• (2) a ratio of each of the distances Da and Db to a diameter De of the circular bottom cloth is 0.5:1 or less.