There are proven studies showing that hemp has the effect of blocking ultraviolet rays. In fact, products made from the original material we use at weavearth have been tested. For example, one material (100% hemp twill fabric, Cocoon Pants in khaki green: photo above) measured a shielding rate of 99% with UPF50+ (the highest rating for UV performance).
So why does hemp material possess this performance? Although this is a highly technical subject, let us explain the reasons behind this function in a simple and accessible way.
1. High lignin content in the fiber structure
Hemp is known to contain a high amount of lignin. Lignin not only has antibacterial properties but also strongly absorbs ultraviolet rays at wavelengths of 280nm, 230nm, and 210nm.
2. Unique fiber structure (porous structure)
Looking at the cross-section of hemp, you can see many overlapping holes. This is called a porous structure. The photo shows the inside of the fiber under an electron microscope at 50 μm (micrometer = 0.001 millimeters).
At the smallest unit of the fibers that make up the yarn, holes called lumens are formed in a tube-bundled structure.
This structure not only creates a thermostat function that regulates moisture absorption and release, but also produces the effects of diffuse reflection (scattering UV rays) and multi-layer refraction (bending UV rays).
This structure is the greatest characteristic of hemp and cannot be replicated with synthetic fibers.
What is surprising is that this UV-blocking function is achieved entirely organically, without relying on chemical agents, because it is derived from hemp’s natural structure.
The long-fiber hemp we rely on is carefully processed to extract the fibers without damaging this structure as much as possible.
On the other hand, conventional cottonized hemp unfortunately undergoes degumming, which removes lignin (because lignin lowers spinning efficiency), and strong alkaline treatment, which destroys the porous structure.
UV protection also depends on fabric design. Gauze weaves and light colors tend to reduce effectiveness, making it essential to match fabric design with product design. Research in this field still has much progress to make.
References (academic papers)
・Structural Characteristics and Processing Technology of Hemp Fiber
Zhang Jianchun, Zhang Hua
(Institute of Quartermaster Equipment, General Logistics Department, Beijing 100082, China)
・Hemp Fiber and Its Development Prospects
倪 燕, 柯 勤飞, 冯 云
(College of Textiles, Donghua University, Shanghai 201620;
Ningbo Entry-Exit Inspection and Quarantine Bureau, Zhejiang Ningbo 315012)
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