The standard “DIN 53350 Plastic films and sheets - Determination of bending rigidity - Two-point method (Ohlsen approach)”, published by the German Institute for Standardization (DIN), describes a test method for measuring the bending rigidity (or stiffness) of plastic films, plastic sheets, and related materials such as coated textile fabrics produced using plastic. This standard includes a procedure for measuring how resistant a thin plastic material is to bending under specific loading conditions. This method is primarily applicable to flexible thin materials such as:
Flexibility and tactile feel (drape, looseness, or resistance to bending) are important quality criteria and are frequently referenced in industries dealing with packaging films, technical textiles, artificial leather (synthetic leather), tarpaulins, flexible membranes, and similar products.
The test principle is the two-point (Ohlsen) method. This method takes its name from the Ohlsen approach and uses a two-point bending mechanism (sometimes described as a load-applied clamp strip). The basic elements of the process are:
This differs from three-point or four-point bending tests (common for rigid plastics or beams) because it is optimized for very thin, flexible materials where large deflections occur and the assumptions of classical beam theory may not be fully applicable.
Stiffness essentially represents the bending moment per unit curvature.
Thickness measurement, especially for plastic films and artificial leather (e.g., DIN EN ISO 2286 series), is often used in conjunction with other DIN/EN/ISO standards such as tensile properties, tear strength, or elongation crack tests.
This is not the same as the more common cantilever method (e.g., DIN 53362 standard for overhang length) or the ISO 2493 standard (paper and cardboard stiffness).
This standard retains its importance in quality control for manufacturers of flexible plastic-based materials, especially in Europe, where DIN standards are widely referenced even when EN or ISO equivalents exist for similar properties.
In short, the DIN 53350 standard includes a method for measuring the bending stiffness of plastic films and sheet materials using a two-point bending approach, commonly referred to as the Ohlsen method. This standard applies to plastic films and sheets, including uncoated and coated films, and describes how to determine the bending stiffness by bending a strip clamped at one end.
In the two-point (Ohlsen) method, the test involves bending a sample of material by applying force at two points (typically a fixed point and the point of force application) to create a controlled bend. This configuration is known as the two-point bending method or the Ohlsen approach. Using this method, the modulus of elasticity (a measure of stiffness) for the film material can be calculated from the bending moment or force measured over a given bending length.
Bending stiffness (also called flexural rigidity) indicates how resistant a thin sheet (such as a plastic film) is to deformation under a bending load. This property is very important in industry and materials science because:
The DIN 53350 standard aligns with these needs by providing clear procedures and measurement principles to ensure that results are consistent and comparable between laboratories and suppliers.
The two-point (Ohlsen) test generally follows these steps:
The DIN 53350 standard also defines test conditions (e.g., sample mounting, bending angle/speed, and repeatability criteria) to improve measurement accuracy and comparability.
The latest update to this standard has modernized the measurement definitions, added terms such as bending force and velocity, and revised the testing equipment requirements, but allowed for other measurement variants while retaining the Ohlsen two-point test in an appendix.
The two-point (Ohlsen) method is one of several bending tests used in material characterization. Other methods include three-point and four-point bending tests, specified in other standards (e.g., ISO 5628) and generally used for stiffer or thicker materials. Furthermore, the two-point approach of the DIN 53350 standard is particularly suitable for flexible films and thin sheets where simpler support configurations may not provide accurate stiffness data.
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