However, these are not “normal” fibers like those that are used for functional clothing, bedding, tea bags or baby wipes. In this factory hall in the middle of a small industrial park, the machines are producing hollow fibers—ultrafine structures similar to macaroni, whose interiors can barely be seen by the naked eye. Each of these fibers can separate two gases from each other by enabling one to diffuse into the fiber’s interior and leaving the other one outside. Under the brand name Sepuran, these plastic straws are packed into thick bunches and built into steel tubes to serve as high-performance filters for the chemical industry and biogas plants. In its most recently developed function, Sepuran is used to purify natural gas, which often contains a large proportion of CO₂ when it emerges from the earth. If the natural gas were used in its unfiltered form, it would quickly erode pipes and connecting pieces.