BREATHABILITY

 Breathability is the ability of a fabric to allow moisture vapor to be transmitted through the material.

 Breathability is measured by the rate at which water vapor passes through in the units of grams of water vapor per
square meter of fabric per 24 hours period (g/m2/d), often abbreviated to just ‘g’. In recent years some of the sporting
goods manufacturers have begun including this information on their labels. Typical mid-range fabric tends to have
values of 5000 mm of water resistance and 5000g of breathability. The highest end materials boast 20000 mm and
20000 g.

 MVTR is the measure of how quickly or how slowly moisture passes through a fabric or other substance. It is usually
measured in g/m²/day. Moisture vapor transmission rate (MVTR), is also referred to as water vapor transmission rate
(WVTR). Breathable fabric is actively ventilated and it passively allow water vapor to diffuse through them yet prevents
the penetration of liquid water.

 Waterproof fabric completely prevents the penetration and absorption of liquid water.

 Waterproof breathable fabric is a material designed to resist liquid water from penetrating while allowing water vapor
(sweat) to escape. This dual functionality keeps the wearer dry from both external rain and internal perspiration.
Waterproof breathable fabrics consist of an outer layer called the “face fabric”, usually made of nylon or polyester, and a
laminated membrane or coating, usually made of PTFE , also known as Teflon® or PU (Polyurethane).
Types Waterproof breathable fabric (WBF)

 Densely woven waterproof breathable fabrics

Probably the first effective waterproof breathable fabric was developed in the 1940s for military purposes and is
known as Ventile. It is made from long-staple, finely combed cotton yarns woven in an Oxford weave, creating a
dense structure with minimal pores. When the fabric gets wet, the cotton fibers swell, reducing pore size and
making the fabric waterproof without chemical finishes. Similar densely woven fabrics can also be made from
micro-denier synthetic filaments under 10 μm in diameter, producing very small pores and achieving waterproof
and breathable properties. The use of very fine fibers and filaments and dense construction results in fabrics with
very small pore size compared with conventional fabrics. Typical pore size for waterproof fabric is about 10 μm
compared with 60 μm for conventional fabric. Ventile fabric has a pore size of about 10 μm when dry and 3-4 μm
when wet. Fabric made from micro-filaments is claimed to have 7000 filaments per cm.

 Membrane/ Laminated waterproof breathable fabrics

Laminated waterproof breathable fabrics made by application of membranes into textile product. These are thin
membrane made from polymeric materials. They offer high resistance to water penetration but allow water vapor
at the same time. The maximum thickness of the membrane is 10 micron.
They are of two types:
• Micro porous membranes
• Hydrophilic membranes.
 The micro porous membranes have tiny holes on their surface smaller than a rain drops but larger than water
vapor molecule. Some of the membranes are made from PTFE(Polytetrafluoroethylene) polymer, PVDF
(Polyvinylidene fluoride). The hydrophilic membranes are thin films of chemically modified polyester
or polyurethane .These polymers constitutes the hydrophilic part of the membrane by forming amorphous region
in the main polymer system. This amorphous region acts as intermolecular pores allowing water vapor molecules
to pass through but preventing the penetration of liquid water due to the solid nature of the membrane.

 Coated waterproof breathable fabrics

Coated fabrics with waterproof breathable fabrics consist of polymeric material applied to one surface of fabric.
Polyurethane is used as the coating material. The coatings are of two types:
• Micro porous membranes
• Hydrophilic membranes.

Microporous coatings have very fine interconnected channels that are smaller than raindrops but larger than
water vapor molecules, allowing vapor to pass through a permanent air-permeable structure. Hydrophilic coatings
also allow vapor transmission, but through adsorption, diffusion, and desorption mechanisms rather than
permanent pores..
Properties Required For Breathable Fabrics

• Optimum heat and moisture regulation (thermo-regularity effect)

• Good air and water vapor permeability.
• Dimensionally stable even when comes in contact to water
• No/Minimum water absorption of the layer of clothing just positioned to the skin.
• Easy care/launderability
• Soft feel, light weight and Durable

Uses of Waterproof Breathable Fabric

• Heavy duty, foul weather clothing: Anoraks, cagoule, packs , hats, gloves, gaiters.
• Foul weather clothing: Survival suits, special military protective clothing, clean room garments, surgical garments,
hospital drapes, mattress and seat covers.
• Fashionable weather protection: rainwater, skiwear, golf suits, walking boot linings, panels and inserts, sport
footwear linings.
• Domestic and transport: Non-allergic bedding, car covers, fire smoke curtains in ships, cargo wraps in aircraft.

Assessment of The Effectiveness of WBF Requires Measurement of Three Properties

• Resistance to penetration and absorption of liquid water

• Wind resistance
• Water vapor permeability