*4.3.2.1. By needling method*

Olry [80] developed a 3D nonwoven process based on the needling method. The method is essentially the same as 2D nonwoven process except for the usage of multiple nonwoven webs for fabric production. These webs are stacked one on top of another and needled in thickness direction to form a thick 3D structure. Figure 39 shows 3D flat and circular nonwoven machines schematically. Fukuta developed a hydroentanglement process where fluid jets are used to produce 3D nonwoven fabric [81].

**Figure 39.** (a) 3D flat non-woven machine (b) 3D circular non-woven machine [80, 81] (c) Schematic view of 3D biaxial‐ ly reinforced nonwoven structure made by warp knitting machine [57].

#### *4.3.2.2. By stitching method*

The 3D nonwoven structure is formed by using a warp knitting machine. Warp yarns are fed by one or more guide bars. Weft yarns are inserted between the warp yarns and the nonwoven web, whereas bias yarns are laid over the warp layers. Multiple compound needles insert the stitching yarns to lock the nonwoven web with warp, weft and bias yarns (Figure 39) [56, 57].
