Polymaker Fiberon PA12-CF10 Nylon Filament Black 0.5kg, Low Moisture Sensitivity PA12-CF Carbon Fiber Nylon 3D Printing 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.