Or put more practically if not more formally correct, it measures how hard
it would have to rain on your bivvy before water started going through the
cover.

If it rained hard enough to pass through sheeting rated at 3500mm
hydrostatic pressure, I would leave my bivvy and other fishing gear behind
and take up a crash course in ark building.


"Baal" wrote in message
...
Waterproofness can be a very subjective term with words like showerproof
and
water resistant sometimes being used . The term hydrostatic head is used
to
denote the amount of pressure of water that is required in order to
penetrate a given fabric. In order to measure the amount of this pressure
a
column of water is pressed against the fabric and the height of the column
is increased until the water penetrates the fabric. The British Ministry
of
Defence definition for a waterproof fabric is that it must resist a column
of water at least eighty centimetres high. Every batch of fabric that is
coated for HORESWARE is tested and must resist a column of water at least
a
hundred and fifty centimetres, that is five feet high. And this is the
minimum acceptable standard. Normally most of our fabrics have hydrostatic
head of at least 300 centimetres and so that after years of use it should
still maintain hydrostatic head of at least 100 centimetres plus.

http://www.horseware.com/faq.asp?FAQ=5

Not being a clever dick. I sound it on a google search. That should
satisfy your curiosity.

--
I smile and go off waving
(Amiably) - for that's my way

Baal

"Baal" wrote in message
...
http://www.awta.com.au/Textiles/Publ...s/pdf/T29B.pdf

--
I smile and go off waving
(Amiably) - for that's my way

Baal

"Richard" wrote in message
...
In specs for bivvys they quote a hydrostatic head, for example 3,500mm
or
5,000mm. Can someone please explain what this means.

Cheers ....... Richard


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