Chapter 12: Waterproof Breathable Fabrics

Author: David A. Holmes

Institution: Department of Textiles, Bolton Institute

12.1 What are Waterproof Breathable Fabrics?

Purpose & Use

 Designed for protective clothing against wind, rain, and loss of body heat.
 Used historically with materials like leather, and later, textile fabrics.

Definitions

 Waterproof Fabric: Prevents penetration and absorption of liquid water.

 Water-Repellent Fabric: Only delays water penetration; not permanent.
 Breathable Fabric: Allows passive diffusion of water vapor while resisting liquid
water.

Historical Methods of Waterproofing

 Early coatings: animal fat, wax, hardened vegetable oils.

 Modern coatings: polyvinyl chloride (PVC), polyurethane.
 Coated fabrics are stiffer and less breathable, suited for emergency use.

Importance of Breathability

 Human body must maintain core temperature (37°C).

 Skin temperature: 33–35°C.
 Core temp below 24°C or above 45°C may cause death.
 Even 34°C or 42°C can cause disorientation or convulsions.

Thermal Regulation & Sweat

 Body cools via insensible perspiration (water vapor).

 Without breathability:
o Increases humidity inside clothing
o Raises thermal conductivity, making clothes uncomfortable
o Can cause hypothermia or hyperthermia
Sweat & Activity

 Sweat required to cool during activity varies with work rate.

Work Rate Sweat Rate

Activity
(W) (g/day)

Sleeping 60 2,280

Sitting 100 3,800

Gentle Walking 200 7,600

Active Walking 300 11,500

With Light Pack 400 15,200

With Heavy Pack 500 19,000

Mountain Walking (Heavy

600–800 22,800–30,400
Pack)

Maximum Work Rate 1000–1200 38,000–45,600

 Body heat loss ability decreases with lower water vapor permeability of fabric.
 Vapour barrier can reduce performance by 60%.
 Firefighters may lose up to 4 litres/hour near fires.
o 1982 US stats: 46.1% of fire deaths were due to heart attacks, not burns.

Breathability Benchmarks

 1991: Claims of >5000 g/m²/day water vapor transmission.

 1998: Claims of 10,000 g/m²/day common.

12.2 Types of Waterproof Breathable Fabric

Main Categories

1. Densely Woven Fabrics

2. Membranes
3. Coatings
1. Densely Woven Fabrics

 Example: Ventile (1940s, military use).

o Developed for pilots in North Atlantic ditching scenarios.
 Made from long staple cotton, woven tightly.
o Yarns: Combed, plied, and Oxford weave (double warp threads).
 When wet: cotton fibres swell, closing pores, preventing water entry.
o No water-repellent finish needed.
 Military-grade Ventile: ~98 threads/cm, ~6000 fibres/cm.
 Civilian versions: lower density, needs water-repellent finish.

Microfilament Synthetics

 Made from polyester or polyamide with <10 µm filaments.

 Does not swell, needs fluorocarbon/silicone finishes.
 Fabric may be windproof, but not waterproof.
 Pore Sizes:
o Conventional fabric: ~60 µm
o Ventile (dry): ~10 µm
o Ventile (wet): ~3–4 µm
o Microfilament: very fine pores, <10 µm

2. Membranes

 Thin films (approx. 10 µm thick) of polymeric material, laminated to textile fabrics for
strength.
 Function: Block liquid water, allow water vapor escape.

Types

A. Microporous Membranes

 Example: Gore-Tex (since 1976)

o Made of expanded PTFE
o ~1.4 billion holes/cm²
o Pore size: 2–3 µm
o Vapor molecule: 0.00004 µm
 Other materials: PVDF, polyurethane
 Sensitive to contamination: body oils, sun cream, dirt, detergent
o Often coated with a hydrophilic PU layer for protection

B. Hydrophilic Membranes

 Solid films (no pores)

  Made from modified polyester or polyurethane
o Contains up to 40% polyethylene oxide
o Allows diffusion of vapor through amorphous molecular regions
 Described as having intermolecular pores (no physical holes)

3. Membrane Incorporation Methods

1. 2-layer laminate (outer fabric + membrane)

o Stiff, rustling feel
o High protection
2. Liner/insert method
o Laminate sewn as liner between layers
o Seam sealing required
3. 3-layer laminate (outer + membrane + inner lining)
o Durable, comfortable
4. Direct Coating
o Membrane coated on textile surface

12.3 Applications of Waterproof Breathable Fabrics

Leisure

 Rainwear: Anoraks, cagoules, ski/golf suits

 Accessories: Gaiters, gloves, hats
 Outdoor gear: Tents, packs, sleeping bag covers
 Footwear: Lining panels and inserts

Work

 Protective clothing: Military suits, cleanroom/surgical gowns

 Medical: Hospital sheets, wound dressings
 Technical: Filtration, packaging, tarpaulins

Domestic & Transport

 Mattress, bedding covers (non-allergic)

 Car covers, airplane cargo wraps
 Fireproof curtains on ships
Here is a comprehensive list of reasoning-based and technical questions with answers derived
from Chapter 12 – Waterproof Breathable Fabrics. These include cause-effect reasoning,
design logic, and application-oriented technical understanding from the text:

REASONING & TECHNICAL QUESTIONS FROM CHAPTER 12

1. Why is breathability important in waterproof garments?

Answer:
Breathability ensures that water vapor (from perspiration) escapes the clothing system. If this
vapor is trapped:

 It increases humidity inside clothing.

 Raises thermal conductivity, reducing insulation.
 Can lead to hypothermia (excess heat loss) or hyperthermia (overheating).
 Maintains wearer comfort and body temperature.

2. Why is waterproof breathable fabric superior to traditional

coated fabrics?

Answer:
Traditional coated fabrics (like PVC or polyurethane):

 Completely block both water and vapor.

 Are stiff and uncomfortable.
 Trap sweat inside the garment.
In contrast, waterproof breathable fabrics:
 Prevent liquid water from entering.
 Allow water vapor to escape, keeping the wearer dry and thermally regulated.

3. Why do firefighters require highly breathable garments?

Answer:
Firefighters experience extreme heat and can lose up to 4L of fluid per hour due to sweat.
If sweat vapor cannot escape:

 Body overheats.
 Heart strain increases.
  Heat stress may cause heart attacks (46.1% of fire-related deaths in 1982 were due to
heart attacks).

4. How does densely woven cotton fabric like Ventile achieve

waterproofing without coatings?

Answer:
Ventile uses:

 Long staple cotton yarns.

 Tight weave with minimal gaps.
 When wet, cotton fibers swell, closing remaining pores.
This creates a barrier to liquid water while still allowing vapor to escape.

5. Why are synthetic microfilament fabrics not truly waterproof

without finishes?

Answer:
Although they have very small pores, synthetic fibres (e.g., polyester):

 Do not swell when wet, unlike cotton.

 Rely solely on mechanical density.
Therefore, fluorocarbon or silicone finishes are needed to achieve water repellency.

6. What is the mechanism of waterproofing in microporous

membranes like Gore-Tex?

Answer:
Microporous membranes:

 Have tiny pores (~2–3 µm).

 These are smaller than rain droplets but larger than water vapor molecules.
 Prevent water entry, while allowing vapor escape.

However, their performance may degrade due to contamination (oils, dirt), so they are often
protected with a hydrophilic layer.
7. How do hydrophilic membranes differ from microporous
membranes?

Answer:
Hydrophilic membranes:

 Have no pores (non-poromeric).

 Transport water vapor via diffusion through the polymer chains.
 Made by blending polyurethane or polyester with polyethylene oxide.
 Less prone to fouling, but rely on chemical transport rather than pore size.

8. Why is a 3-layer laminate better than a 2-layer or liner system?

Answer:
A 3-layer system (outer + membrane + inner lining):

 Offers durability, comfort, and protection.

 Reduces rustling and stiff feel found in 2-layer systems.
 Better for high-performance and long-use garments.

9. What are the four main methods of incorporating membranes

into clothing?

Answer:

1. 2-layer laminate: membrane bonded to outer fabric (good protection, less comfort).
2. Liner/Insert method: membrane as separate inner layer (softer, needs seam taping).
3. 3-layer laminate: outer + membrane + lining (balanced comfort and protection).
4. Direct coating: membrane applied directly to fabric (cost-effective).

10. Why does body performance reduce with low fabric

breathability?

Answer:
Lower breathability means:

 Less sweat vapor escapes.

 Core body temperature rises.
  Performance drops; in tests, up to 60% reduction was noted when using vapor-barrier
clothing.

11. Why is cotton used in Ventile rather than synthetic fibres?

Answer:
Cotton:

 Swells when wet, reducing pore size.

 Achieves natural waterproofing without coatings.
 Maintains good breathability.
Synthetic fibers, though fine, do not swell, and need chemical treatment to be
waterproof.

12. What are the advantages of hydrophilic membranes over

microporous ones?

Answer:

 No pores to clog = better durability.

 Less affected by contaminants.
 More consistent performance over time.
 However, less breathable under dry conditions than microporous membranes.

13. Why is it essential to maintain fabric water vapor permeability

for athletes or laborers?

Answer:

 Enables efficient sweat evaporation.

 Prevents overheating or heatstroke.
 Maintains hydration balance.
 Increases endurance and safety during exertion.
14. How does the poly(ethylene oxide) component in hydrophilic
membranes help vapor transport?

Answer:

 It forms hydrophilic paths in amorphous polymer regions.

 Attracts and facilitates water vapor diffusion.
 Works like a molecular sponge, drawing vapor through the film.

15. Why must microporous membranes be laminated with

protective PU layers?

Answer:

 Micropores are vulnerable to blockage by body oils, dirt, and chemicals.

 PU layers:
o Act as contamination shields.
o Maintain membrane integrity.
o Enhance durability and lifespan.

Here is a structured summary of the technical knowledge from Chapter 12 – Waterproof

Breathable Fabrics, including key definitions, mechanisms, material properties, and
engineering principles:

Technical Knowledge from Chapter 12 – Waterproof

Breathable Fabrics

1. Key Definitions
Term Definition

Waterproof Completely blocks liquid water penetration.

Delays but doesn’t fully block water entry. Short-lived

Water-repellent
durability.

Breathable Allows water vapor to pass through; not ventilated by

 Term Definition

air.

Water Vapor The ability of a material to allow sweat vapor to pass

Permeability outward.

Microporous Membrane with microscopic pores that block water but

Membrane allow vapor escape.

Hydrophilic Solid film that transports water vapor via diffusion

Membrane through the polymer.

2. Fabric Construction Methods

A. Densely Woven Fabric (e.g., Ventile)

 Material: Long staple cotton

 Yarn: Combed, plied for parallel fibre alignment.
 Weave: Oxford weave – plain weave with dual warp yarns.
 Function: Swelling of cotton fibres when wet reduces pore size, increasing
waterproofing.
 Pore size (wet): 3–4 µm
 No coating required for waterproofing (in high-density types).

B. Microfilament Fabric

 Material: Synthetic fibres (polyester or polyamide)

 Filament diameter: <10 µm
 Performance:
o Windproof
o Needs silicone or fluorocarbon finish to be waterproof.
o Does not swell; relies on physical tightness of weave.

3. Membrane Technologies
Microporous Membrane (e.g., Gore-Tex)

 Material: Expanded PTFE (ePTFE)

 Pore size: ~2–3 µm
 Structure: Billions of tiny pores allow vapor molecules (0.00004 µm) to escape.
 Needs protection from fouling (e.g., PU outer layer).
Hydrophilic Membrane

 Materials: Chemically modified polyurethane or polyester

 No physical pores.
 Vapor transport via diffusion through amorphous molecular regions.
 Hydrophilic segments (e.g., polyethylene oxide) attract water vapor.

4. Water Vapor Transport Mechanisms

Mechanism Description

Microporous
Vapor moves through physical pores (size-controlled barrier).
Flow

Hydrophilic Water vapor moves molecule-by-molecule via hydrogen

Diffusion bonding and chain mobility in polymer matrix.

5. Sweat and Heat Production

Power Output Sweat Rate
Activity
(W) (g/day)

Sleeping 60 2,280

Heavy Pack
500 19,000
Trekking

Max Work 1000–1200 38,000–45,600

 Clothing must accommodate vapor transmission proportional to sweat output.

 Standard breathability: >10,000 g/m²/day for high-performance garments.

6. Integration Methods of Membranes

Method Layers Properties

High protection, less comfort

2-layer laminate Outer + membrane
(rustling).

Insert (liner) Separate laminated More comfortable, requires seam

method insert sealing.
 Method Layers Properties

Outer + membrane +
3-layer laminate Balanced protection and wearability.
lining

Membrane coated on Inexpensive, durable for simpler

Direct coating
fabric applications.

7. Pore Size and Fiber Packing Comparison

Material Pore Size Notes

Conventional fabric ~60 µm Not waterproof.

Ventile (dry) ~10 µm Shrinks when wet.

Water resistance increases

Ventile (wet) ~3–4 µm
dramatically.

ePTFE membrane (Gore-

~2–3 µm Microporous, vapor permeable.
Tex)

~0.00004 Can diffuse through even non-

Water vapor molecule
µm porous film.

8. Factors Affecting Performance

 Fibre Swelling (in natural fibres like cotton): closes pores.

 Fouling/Contamination:
o Affects microporous membranes negatively (oils, salts, lotions).
 Finishing Treatments:
o Fluorocarbons/silicones improve repellency.
 Laminate Structure:
o Affects stiffness, handle, and water resistance.

9. Engineering Design Considerations

 Comfort vs. Protection Trade-off:

o Higher waterproofing usually reduces breathability.
 Moisture Management:
o Multilayer systems needed to balance vapor transfer and insulation.
  Durability:
o Hydrophilic membranes resist fouling better than microporous ones.
 Applications:
o Design depends on intensity of user activity and exposure duration.

10. Real-World Performance Criteria

 Water Resistance: Measured via hydrostatic head (in mm water column).

 Vapor Permeability: Measured in g/m²/day or g/hr/m².
 Durability: Affected by abrasion, laundering, and environmental exposure.
 Seam Sealing: Essential for membrane-based garments to maintain waterproof integrity.

Would you like this compiled with the earlier Q&A into a printable PDF? I can do that next.