TPU film and TPU mobilon: Twin materials of the same origin but different properties
When designers encounter TPU film and TPU elastic mobilon at fabric shows, they often mistakenly believe the difference lies solely in thickness. In reality, from molecular arrangement to end-use application, the two diverge. This difference stems from a fundamental difference in production processes: TPU film is produced on a precision cast-film production line, where molten polyurethane is spread like liquid crystal onto a stainless steel belt. Three rollers calender the material to form a uniform, thin layer with a thickness tolerance of ±0.01mm, a process similar to casting an optical lens. TPU elastic, on the other hand, undergoes an extrusion process: the high-temperature melt gushes out of a circular die, passes through a water-cooling tank for instant shaping, and then undergoes biaxial stretching to impart elasticity. The process is more like blowing a glass tube, with the molecular chains oriented along the direction of stretching.
This difference in manufacturing DNA is manifested in its physical properties. The cast film's nature enables it to achieve ultra-thin thicknesses as thin as 0.1mm and can be freely slit up to 2 meters wide, providing invisible armor for waterproof and breathable clothing. In contrast, extruded elastic tape, for wide widths (e.g., over 20mm), are constrained by shrinkage during cooling, limiting thicknesses to 0.3mm or less, otherwise cross-sectional deformation may occur. The surface texture further reveals its origins: the film's surface is as smooth as silk (roughness Ra ≤ 0.05μm), suitable for fine processing such as laser etching. The extruded strip retains micron-scale longitudinal flow lines, an imprint of the melt flow within the die.
The most critical gap lies in elasticity. Because the molecular chains of film are arranged in a planar network, stretching primarily relies on changes in molecular bond angles. This results in a rebound rate of less than 70% after 300% elongation, making it prone to permanent wrinkling after repeated stretching. Elastic bands, on the other hand, undergo a subsequent twisting process, where the molecular chains are coiled like a coiled spring, achieving a high rebound ratio of 1:3. Even after 5,000 stretches, they retain 90% shape memory. This explains why waterproof tape on jackets uses film for static sealing, while yoga pants waistbands must utilize elastic bands to accommodate dynamic deformation.
When the two materials are juxtaposed on a lab bench, their fates become clear: the film is a silent guardian, shielding against wind and rain with its 0.15mm thickness at the expense of flexibility; the elastic tape is an active supporter, performing the art of elasticity within a millimeter-thick cross-section. Understanding this difference is like understanding the invisible grammar of modern functional clothing—between the laminated lining of an outdoor jacket and the breathable hem of a sports bra, a shared yet distinct material philosophy flows.
