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.
Read more on our BLOG.
Articles in this section
- 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?
- What does IPX8 mean?
- Is the external pocket of the rapid / flow dry pack waterproof?
- Hydrostatic head - what does it mean?
- I want to place my phone/camera/laptop in a dry bag, which one is the best to use?