Tyvek is labeled as "water resistant" and not "water proof", but I'd really love to know how much is the fabric resistant to water in practice.

Some people built tarps or even tents out of it, but I was not able to find any tests result of the actual water resistance of the fabric - or better, of the fabrics, since there's more than one version of it.

Is there any information about how much rain could a tyvek sheet actually take before starting to leak? Did anybody made any tests? Thank you so much.

EDIT. Thank you so much for those values, I missed them. But still, can you please describe how do those numbers relate to actual outdoors (that means, rain) practice? For instance, is "15" a light rain for about one hour? Is "1016" comparable to heavy rain for several hours non stop? I'd love to get an idea in simple terms of rain if that's somewhat possible and if anybody has an experience with it.

  • As a side note tents/tarps are rarely 100% waterproof. They water is designed to run down the outer, so it's doesn't matter if some water get's though the outer, providing the person inside the inner doesn't get wet – Liam Nov 14 '14 at 16:43
up vote 4 down vote accepted

As you stated in your question, there are many different Tyvek fabrics, some are only water resistant, whereas others are completely waterproof (such as is used for express mail envelopes and printing materials). There are lots of forums online that discuss the use of Tyvek tarps for backpacking, to determine how water resistant your fabric is you need to know which fabric you have.

The post below is from the thread, "Is Tyvek Truly Waterproof?" at www.backpackinglight.com

Tyvek waterproofness depends on the style

Hydrostatic head is a measurement of how waterproof a fabric is. It refers to the height of a water column the fabric can support before leaking. It depends on which Tyvek style you purchase as to what the hydrostatic head is. The inches hydrostatic head is less than 15 (water resistant) except for the following styles: Homewrap = 82.7, 1025BL = 53, 1059B = 56, 1073B = 59, and 1422A = 40.

The above values are in inches H2O; to convert to mm H2O, multiply any of the above in H2O values by 25.4. Other than the following exceptions, Tyvek versions are less than 381.0 mm H2O (water resistant at best):1025BL = 1346.2, 1059B = 1422.4, 1073B = 1498.6, and 1422A = 1016.0. Homewrap, which has printing, is 2100.0.

Unlike most light shelter materials, Tyvek maintains its original HH head through multiple wash cycles. You can compare these Tyvek mm H2O HH values with the common light weight shelter materials mm H2O HH I tested in the thread http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=45026

Rain resistance is measured and expressed as hydrostatic head in millimetres (mm). This indicates the pressure of water needed to penetrate a fabric. Heavy or wind-driven rain has a higher pressure than light rain. Standing on a groundsheet increases the pressure on any water underneath. Fabric with a hydrostatic head rating of 1000 mm or less is best regarded as shower resistant, with 1500 mm being usually suitable for summer camping. Tents for year-round use generally have at least 2000 mm; expedition tents intended for extreme conditions are often rated at 3000 mm. Where quoted, groundsheets may be rated for 5000 mm or more.

Wikipedia: Tent-General Considerations

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