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With a carbon neutrality horizon in 2050 as target for the industry, the use of growing quantities of recycled and recyclable materials is key. “Greenflocks” chips urethane based poroelastic material coming from recycled PU mattresses, that are decontaminated, shredded, mixed with thermoplastic bi-component PET fibers as well as thermofixed with hot air ovens resulting in low Volatile Organic Component (VOC) and odors, seems to be a good candidate. Indeed, one gets a 80 % recycled poroelastic material, 100% recyclable, with mechanical and acoustical properties allowing between 10 % and 20 % weight reduction compared to shoddy cotton felt typically depending on the density. Indeed, this “Greenflocks” material presents excellent mechanical decoupling properties even at high densities for the low thickness areas above 150 kg/m3 and up to 300 kg/m3 typically with a Young’s modulus kept below 150 kPa.

The lightweighting research on noise treatments since years tends to prove the efficiency of the combination of good insulation with steep insulation slopes with broadband absorption, even in the context of bad passthroughs management implying strong leakages. The real issue lies more in the industrial capacity to adapt the barrier mass per unit area to the acoustic target from low to high segment or from low petrol to high diesel sources, while remaining easy to manipulate. The hybrid stiff insulator family can realize this easily with hard felts barriers backfoamed weighting from 800 g/m2 to 2000 g/m2 typically with compressions below 10 mm. Above these equivalent barrier weights and traditional compressions of 7 mm for example, the high density of the felts begins to destroy the open porosity and thus the absorption properties (insulation works anyway here, whenever vibration modes do not appear due to too high stiffness…).