Imagine a vertical tube with a fabric sample clamped at the base so that no water can escape – now add water. The height of the column of water in millimeters at the point where the water forces its way through the fabric/coating is called the hydrostatic head.
There is no internationally accepted standard for how high this should be for a ‘waterproof’ fabric.
In real-world terms, a dry bag intended for use inside a backpack will only require a modest hydrostatic head; a dry bag intended for paddling will need a much higher hydrostatic head.
Ultra-Sil tests at over 2000mm (more waterproof than some tent floors), which is perfectly adequate for waterproof storage inside a pack, but not sufficient for use in paddle situations. A dry sack intended for paddling will need a hydrostatic head of 10,000mm.
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Articles in this section
- Does the Meridian Duffle have internal compartments?
- Is the Meridian Duffle waterproof?
- Is the Meridian Duffle carry-on compatible?
- Which dry bags are compatible with the Dry Bag Sling?
- What is the Ultra-Sil Shopping Bag?
- What is the weight limit of what I can carry in the ultra-sil and ultra-sil nano day packs?
- Which dry bags/sacks are appropriate for external use? (i.e. not inside another bag or pack)
- I have a hole in my stuff/compression sack, is this covered under warranty?
- Do I really need to "double bag" my phone when using a dry sack/bag?
- What size compression sack do I need for my sleeping bag?