Synthetic Leather
Foaming is how synthetic leather gets its hand and loses three quarters of its polymer bill at the same time.
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Neat polymer density over foamed density
Expansion trades polymer for air, and mechanical properties go with it — tear, abrasion and peel from the base cloth all fall as the void fraction rises. Cell structure matters as much as density: the same expansion with coarse open cells behaves nothing like fine closed ones.
Artificial Leather PU Foam Expansion & Density Calculator — free, with the formula and a worked example, at Textile School.