Polymaker TPU Filament Grey, 0.75kg Shore 90A Flexible 3D Printer Filament - PolyFlex TPU90 3D Printing TPU Filament 0.75kg Grey Soft Flexible Filament

The most engineering-minded consumer brand in this space. Polylite is their everyday PLA, PolyMax adds impact resistance, and PolyWood nails the timber look. They publish data sheets and actually explain what's in their formulations.