**6.1. Energy or pressure absorption**

Energy or pressure absorbed (%) by padding decreases with increase in mass per unit area of padding (Figure 8a). This is due to the fact that the increase in mass per unit area leads to availability of more number of fibres for sharing the compressive load. Availability of more fibres increases entanglement during preparatory methods, and this causes more frictional resistance to prevent fibre-to-fibre slippage during compression load-recovery test. Reduction of fibre slippages minimizes the permanent deformation in compression-load recovery test. Therefore, lower energy absorption is obtained for higher mass per unit area of padding. Furthermore, the amount of energy loss decreases with increasing needling density (Figure 8b). Increase in needling density also stimulates more entanglement of fibres, which causes the compact and stiff structure of padding [42, 43]. This avoids fibre-to-fibre slippages during compression; hence, there will be low energy or pressure absorption for a stiff padding compared to soft padding. In real scenario, the use of a heavy and stiff padding should be avoided as it would not be able to absorb the excess pressure at critical regions. If comparing different fibres, it can be concluded that the energy absorbed is less for padding composed of thinner fibre than coarser fibre (Figure 8c). Thick or coarse fibre has less specific area compared to thin fibre, due to which the frictional resistance within the porous network of padding will be lesser for thick fibre compared to thin fibre. Moreover, padding made from coarser fibre has more porous structure. This all results in more energy absorption and therefore more pressure reduction for the padding made from higher fibre linear density compared to lower fibre linear density.

**Figure 8.** Effect of structural parameters of nonwoven on pressure absorbency: (a) effect of mass per unit area (50E4 punches/m2 ; 2.5 denier); (b) effect of needling density (100 g/m2 ; 2.5 denier); (c) effect of fibre denier (100g/m2 ; 130E4 punches/m2 )
