PURPOSE: To obtain the title material useful as printed circuit board, etc., having high resin impregnating properties by passing glass fibers under tension in a turbulent flow zone of gas, forming glass fibers alternately having opening parts and interlacing parts in the fiber direction and weaving.

CONSTITUTION: A filament raw material of glass fibers is fed from glass yarn 11 through guides 12 and 13 to a feed roll 14, sent to a turbulent flow zone of gas or vortex flow zone of interlacing device 5, processed under tension by a delivery roll 16 to form glass fibers alternately having opening parts l2 and interlacing parts l1 in the fiber direction and wound into a pirn 19 by a take-up roll 18. Then the glass fibers are used as warp or weft and woven into glass cloth to give the aimed glass cloth having ≤three times as long diameter of the opening part l2 of the fibers in the glass cloth as the diameter of the interlacing part l1.