US Patent 7578317 High-speed spun-bond production of non-woven fabrics

In combination with a high-speed spun-bond apparatus, rather than using a circulating sieve belt for collecting the stretched filaments and forming the web, a fabric having a 4-shed double layer with support shute weave design is used. This fabric is commonly referred to as a 4B weave and 4B weave with stuffer in center. In general, the fabric has a permeability ranging from 400 to 800 cfm with a woven or pin seam where the seam permeability and caliper varies only slightly with respect to the rest of the fabric.