Flexible material, often referred to as TPU or "thermoplastic polyurethane", is a type of printing string for 3D printers whose main characteristic is flexibility and pliability. The resulting prints behave much like rubber - they can be bent, squeezed and stretched without breaking. For this reason, it is used to produce objects that require flexibility, impact resistance or vibration damping. Typical examples are protective phone covers, flexible seals, tyres for models or functional parts that need to bend. Printing with this material is more challenging than with rigid filaments. Due to its softness, there can be problems when moving the material into the print head. For reliable printing of flexible materials, printers with a so-called 'direct drive' extruder are preferable, where the feed mechanism is located directly above the nozzle, which shortens the filament path and reduces the risk of filament jamming. It is also usually necessary to print at a significantly slower speed and carefully set the parameters for filament reversal, known as retraction.
