Tensile strength testing and comparison of Sheertex fibers and steel
Senior Staff Technologist
SAMIRA KHAJEHI, BSC MBA
VP Corporate Strategy
To showcase strength, one of the most com- monly used comparator reference materials is steel due to its well-documented strength properties. SRTX Labs developed a methodology to compare the polymer found in the Sheertex knit against steel, accounting for variables such as material density and difference in cross-sectional area, an important factor in determining tensile strength. Ultimately, the Sheertex polymer was shown to be more than ten times stronger than structural steel.
Hosiery is a multi-billion dollar industry with billions of pairs of tights sold worldwide each year . These tights are largely subject to similar types of wear and tear, namely snags, tears, and holes . At Sheertex, we believe that if garments were made of stronger materials, more durable products would be made, allowing consumers to wear them for longer. If consumers can get more wears from their pairs of pantyhose, fewer should end up in landfills. Given the scale of the entire industry, even doubling the inherent strength and durability would amount to a significant reduction in post-consumer waste.
Using a polymer typically reserved for high performance applications like bulletproof vests and climbing equipment, Sheertex formulated a knit that was sheer and stretchy enough for hosiery.
To ensure that the polymer’s strength was not compromised by making it sheer and stretchy, SRTX Labs compared the strength of its fibers against several varieties of steel.
Some challenges arise when comparing tensile strength of such drastically different materials. Yarns used in sheer hosiery are extremely small in diameter—well under a tenth of a millimeter—and are often multifilament. These properties make devices like outside micrometers or calipers unhelpful in determining the critical cross-sectional area of the material, meaning other methods are needed to get results with a reasonable degree of certainty.
Ultimately, a tensile strength in the form of grams per mm2 was produced for the Sheertex polymer yarn using a machine adhering to ASTM D2256 . In the case of steel, comparator values were sourced from a reputable publication identified during a literature review. This allowed for a like- for-like comparison of strength values when looking at relative measurements per material.
We predict that when compared to structural steel, the tensile strength of Sheertex fibers is at least ten times as strong.
For the in-house fiber testing, an Instron 34SC-1 single- column tester was fitted with a 50 N load cell and pneumatic yarn grips (catalog number 2714-031), A test plan for ASTM D2256  was followed. For denier and cross-sectional area measurements, an OHAUS AX423/E microgram scale was used, with a resolution of 0.001 g.
Five meters of Sheertex yarn was placed into the microgram scale and weighed. Next, 250mm of each cut sample was clamped into the Instron test machine. The ASTM D2256 test method was run on the samples to determine how many Newtons of pulling force were required to break the sample. All samples were observed to break at the midpoint and not around the clamping apparatus, indicating that the fabric’s tensile strength was accurately measured. To correlate the break force to cross-sectional area, the weight of the sample was first multiplied by the relative density of the material to obtain the sample’s volume. Then, each sample yarn’s radius was calculated, assuming a perfect cylinder. The cross- sectional area of the sample was finally calculated in mm2 using the radius.
Steels which are defined by their tensile properties were selected as comparators, namely S275JOH ‘structural mild steel’ and 500B rebar used in reinforced concrete designs.
The average weight of the samples, combined with their relative density, was used to determine the cross-sectional area of the sample for the purposes of determining the ultimate yield strength of the materials in MPa. Results for these calculations and also the ultimate yield strength of the yarn is visible in Table I:
PHYSICAL PROPERTIES OF FIBER SAMPLE
Using these values, along with yield strength values for common structural steels—here we have selected S275 and B500—we can then construct a like-for-like comparison of the relative strength of Sheertex fiber and structural steels.
Fig. 1. Comparison in MPa of materials , 
The stark difference in strength present in the Sheertex fiber vs. all other compared materials is evident. Specifically, it is 13.1times stronger than S275 structural steel, and 7.21times stronger than B500 (rebar) steel.
Steel is a material that is known for its strength due to its common usage in construction and vehicle fabrication. The fiber used in the Sheertex knit is undeniably stronger than steel, by a factor of more than ten. The strength of Sheertex hosiery means fewer torn fibers, making its products more durable and longer-lasting.
Many thanks to Amy Dam, Amanda Fleury, and Charlotte Fauqueux for their assistance with editing and adding clarity to this report.
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THIS WORK IS FUNDED BY SRTX LABS.