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The hydrostatic head rating is a measure of the water resistance of fabrics, including PU (Polyurethane)-coated fabric. This rating indicates the height of a water column that the fabric can withstand before water begins to penetrate through. The determination of the hydrostatic head rating involves subjecting the fabric to controlled water pressure and measuring the point at which water starts to penetrate.
Testing Methodology:
During the hydrostatic head test, a sample of the PU-coated fabric is placed over a cylindrical column. The fabric is then subjected to increasing water pressure by gradually filling the column with water. The test continues until water visibly penetrates the fabric or the specified pressure level is reached. The height of the water column at the point of penetration determines the hydrostatic head rating.
Common Ratings:
The hydrostatic head rating is typically expressed in millimeters of water (mm H₂O). Common ratings for PU-coated fabrics can vary, but they generally fall within the range of 1,000 mm to 20,000 mm or more. Here's a general breakdown of hydrostatic head ratings and their implications:
Low Resistance (1,000 mm - 5,000 mm):
Fabrics with lower hydrostatic head ratings are suitable for light rain and everyday use. They provide basic water resistance but may not be suitable for prolonged exposure to heavy rain or severe weather conditions.
Moderate Resistance (5,000 mm - 10,000 mm):
Fabrics in this range offer moderate water resistance and are suitable for activities in moderately wet conditions. They can withstand light to moderate rain for extended periods.
High Resistance (10,000 mm - 15,000 mm):
Fabrics with higher hydrostatic head ratings are considered highly water-resistant. They are suitable for activities involving exposure to heavy rain and wet environments, making them ideal for outdoor pursuits in challenging weather conditions.
Very High Resistance (15,000 mm and above):
Fabrics with very high hydrostatic head ratings are designed for extreme conditions. They provide exceptional water resistance and are suitable for activities such as mountaineering or prolonged exposure to heavy rain.
It's important to note that the choice of hydrostatic head rating depends on the intended use of the fabric. Outdoor enthusiasts may choose fabrics with higher ratings for more demanding activities, while everyday outerwear may have lower ratings. Manufacturers often specify the hydrostatic head rating of PU-coated fabrics in product descriptions to help consumers make informed decisions based on their specific needs and anticipated weather conditions.
