Hollow fibers made of polyester have a long history as an animal-friendly alternative to classic down and feather core fillings for bedding such as blankets and pillows. Hollow fibers as filament yarns, on the other hand, have barely made a splash in the bedding sector up to now. Mattes & Ammann® GmbH & Co KG, a Baden-Wuerttemberg based specialist for textile fabrics changes this situation. The special yarn cross-section of these hollow fibers has cavities in the individual filaments over the entire yarn length. The air trapped in the yarn as a result of these cavities has a naturally insulating effect, much like the natural fur of polar bears. In mattresses and bedding, it will improve the user's sleeping comfort while stabilizing his/her body temperature even during ambient temperature peaks.