What is ‘Hydrostatic Head’ and how does it help my bivvy to perform?

‘Hydrostatic Head’ is a technical measurement of the water proof level of your bivvy. It measures the amount of pressure required to force water through the bivvy fabric.

The higher the Hydrostatic Head number = more pressure required to force water through the fabric = the better the waterproof effect of the fabric = the drier and more comfortable our customers are when using our bivvies.

Our bivvies are engineered to give market leading levels of hydrostatic head – so the best waterproof effects of any bivvies on the market.

This best in class level of waterproof effect built into the fabrics supported by the specialist tape sealing you will see in each and every bivvy manufactured by our company. This highly technical seal has been developed to prevent any leakage of the bivvy at any sewn joint in the bivvy construction.

Why does the rain ‘bead up’ and run off my bivvy?

This is due to the durable water repellent (DWR) finish which is applied to the surface of the fabric exposed to rain during use.

This special invisible chemical shield causes the rain droplets to bead or ball up and run off the surface of the bivvy so keeping the bivvy outer fabric drier for longer.

The protective shield is also repellent to oil based materials and so will help to keep your bivvy looking cleaner and newer for longer.

This surface run-off effect also helps our Aquatexx® fabric breath more efficiently.

The initial beading up and run off of rain seems to lessen after longer rain showers or in constant rain – why is this and is it a problem?

The overall protection from rain is a combination of the fabric treatment and the specialist technical coating. The outer fabric water repellency is designed to be the first line of defence to repel the rain and the coating is there as an impenetrable layer to give 100% waterproof effect.

Even though after longer periods of rain the water will start to slowly wet the fabric surface do not worry, this does not mean any water will penetrate through the fabric as the coating is there to prevent this from happening, it’s the second line of defence and will ensure you stay dry even in the worst of conditions.

Once the bivvy is thoroughly dried the outer water repellency will return and over time can be refreshed by using the Revive Shelter Re-Proofer Kit.

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