|
|
 |
| Waterproof and
breathable - Why both ?
Elemental protective outerwear needs to
be both waterproof AND breathable. A totally waterpoof
but non-breathable garment would be very uncomfortable
to wear, as perspiration (as water vapour) would have
no means of escaping, thus condensing on the inside
of the garment, leaving the wearer 'wet from within'
and feeling cold.
Conversely a very breathable but non-waterproof
garment would be so open, allowing air, and perspiration
(as water vapour) to pass freely through, that it would
offer little protection from the elements (e.g. canvas
tents let water through if you lean against them!) |
 |
|
|
|
| Types
of Waterproofing ...
There are two commercial ways to make
a fabric resist water:
|
 |
|
|
|
 |
| Introduction ...
There are two types of polyurethane film
used to make waterproof breathable products:
1. Microporous ...
Microporous films are full of microscopic
holes or pores. These pores are approximately 5 microns
in diameter whereas water droplets are typically 500
- 5000 microns and 'drizzle' droplets can be as small
as 200 microns in diameter and are therefore too large
to penetrate the pores in the film. It is impossible
for water droplets to pass through, and therefore the
film is 100% waterproof.
|
|
|
|
| |
0.0003 |
5 |
200+ |
| |
1 |
10,000 |
1,000,000 |
Water vapour molecules, generated by the
body perspiring, are much smaller (typically less than
0.0003 microns) and pass easily through the holes, carrying
moisture away.
|
|
|
|
| 2. Hydrophilic
...
SealSkinz® socks and gloves use a
different type of membrane called hydrophilic ("water
loving"). Hydrophilic membranes are totally solid,
without pores. It is therefore physically impossible
for droplets of liquid water to pass through the membrane,
however, it is breathable because water vapour molecules
are transmitted from molecule to molecule through the
membrane on the polymer chain and expelled on the other
side. The driving forces are the differences in humidity
and temperature between the atmospheres on each side
of the film.
The internal climate, next to the skin,
is hot and humid because the body is generating heat
and moisture as it exercises. The external climate is
much drier and cooler. Consequently water vapour is
driven from the inside of the garment to the outside.
As the foot gets hotter during an activity, so the film
becomes more efficient at expelling moisture. |
|
|
|
|
| SealSkinz®
100% Waterproof Testing …
Every single SealSkinz® product is
tested before it leaves the factory. The sock or glove
is mounted onto a machine which subjects it to water
pressure. If any product leaks, the item is rejected
and diced. Every SealSkinz® product is therefore
guaranteed to be 100% waterproof.
The waterproof film can withstand 10psi
of hydrostatic head pressure, the equivalent of a column
of water 700cm high standing on the fabric surface.
This is 7 times the level required to meet European
Standards for waterproof clothing.
|
|
|
|
|
| Breathability
Index.
Breathability is measured by a water vapour
permeability index in accordance with BS 3424: Part
34: 1992 Method 37. In this test, pieces of laminated
fabric cover a small cup holding a measured mass of
water.
The cup is allowed to stand in a controlled
climate for several hours. At the end of the test, the
cup is re-weighed to determine how much moisture from
within the cup has evaporated and been expelled through
the sample fabric.
A water vapour permeability (WVP) rating
is then determined by comparison to a standard fabric
given the same treatment. The SealSkinz® Mid
light, Long light, Mid thermal and the New SealSkinz
Glove all have a water vapour permeability index
of 50-60% when measured in accordance with BS 3424:
Part 34: 1992 Method 37.
|
|
|
|
| 
An Adobe® Acrobat "PDF" version of this
page is available, should you need this information
off-line for printing etc. Click
here to download it
|
|
|
|
|
|
 |
