News

What is a waterproof and breathable membrane?

Waterproof and breathable membrane is a new type of polymer waterproof material. The following will provide a detailed introduction from the aspects of its structural composition, working principle, performance characteristics, application fields and production processes:

• Structural Composition

◦ PP Spunbond Non-woven Fabric: Usually used as the inner and outer layers of the waterproof and breathable membrane. It is a mesh fiber material made by melt spinning process, with up to 3000 fibers per square centimeter and a breaking strength of more than 50N/cm². It has good flexibility and strength, can resist mechanical damage during construction, remains stable in the temperature range of -40℃ to 120℃, and plays a role in enhancing tensile strength, hydrostatic pressure and protecting the middle layer.

◦ PE Polymer Breathable Membrane: Located in the middle layer of the waterproof and breathable membrane, with a thickness generally ranging from 0.02 to 0.03mm. It forms a microporous structure through a biaxial stretching process, with the micropore diameter controlled between 0.1 and 0.2 microns, which is smaller than the minimum diameter of liquid water (about 20 microns) and much larger than water vapor molecules (0.0004 microns). It is the key layer for realizing selective permeability. High-quality PE breathable membranes can have a water vapor transmission rate of up to 8000g/m²・24h and a hydrostatic pressure value exceeding 20000mmH₂O.

◦ Special Application Membranes: In some special application fields, there are more excellent membrane materials such as EPTFE membranes. EPTFE membrane is a microporous membrane formed by expanding and stretching polytetrafluoroethylene raw materials, with a porosity of more than 85% and an aperture distribution uniformity error of less than ±0.02 microns. Compared with traditional PE membranes, while maintaining the same breathable performance, its chemical corrosion resistance is increased by 5 times, and its service life is extended to more than 15 years.

• Working Principle

◦ Water Vapor Penetration Principle: In the state of water vapor, water particles are very small. According to the principle of capillary movement, water vapor can smoothly penetrate to the other side of the capillary, thus causing a vapor-permeable phenomenon.

◦ Waterproof Principle: When water vapor condenses into water droplets, the particles become larger. Due to the effect of surface tension of the water droplets, water molecules "pull and counteract" each other, so water molecules cannot smoothly break away from the water droplets and penetrate to the other side, preventing water penetration and endowing the breathable membrane with waterproof function.

• Performance Characteristics

◦ Waterproofness: It can effectively block the penetration of liquid water, and can maintain good waterproof effect even under high water pressure. For example, when used in building walls, it can prevent rainwater from penetrating into the wall.

◦ Breathability: It allows water vapor to pass through, so that the water vapor inside the protected space can be discharged, maintaining air circulation and dryness. For example, in outdoor sportswear, it can discharge the sweat generated by the human body.

◦ Weather Resistance: It has good anti-aging and anti-ultraviolet properties, can be used for a long time under different climatic conditions, maintains stable performance and prolongs service life.

◦ Chemical Corrosion Resistance: It is resistant to most chemical substances, not easily eroded by acids, alkalis and other chemical substances, and can be applied in chemical, medical and other fields.

• Application Fields

◦ Construction Field: Used in the walls and roofs of steel structure and wood structure buildings, it can strengthen the air tightness and water tightness of the building, and at the same time, quickly discharge the water vapor inside the structure, avoid the growth of mold in the structure, and protect the thermal performance and durability of the building.

◦ Clothing Field: Such as 冲锋衣，mountaineering clothes and other outdoor sportswear, which can prevent rain and discharge the sweat generated by the human body, keeping wearing comfortable.

◦ Medical Field: It can be used in medical supplies such as surgical gowns and protective clothing to prevent liquid penetration, and at the same time allow water vapor to pass through, keeping the working environment of medical staff comfortable.

◦ Electronic Field: Ultra-thin waterproof and breathable membrane components are implanted in the speaker holes of smart watches, mobile phone SIM card slots and other parts, which not only retain clear sound transmission, but also achieve complete airtight protection, protecting the internal components of electronic equipment from water vapor erosion.

◦ Automotive Field: The battery pack in the power system of new energy vehicles can timely release the gas expansion generated during charging and discharging through the waterproof and breathable membrane, avoiding deformation or explosion of the sealed shell due to excessive pressure difference.

• Production Process

◦ Hot Press Composite: It is the main process for producing real waterproof and breathable membranes at present. It does not contain glue, can withstand temperatures above 110 degrees, has high strength and anti-aging properties, and the product can meet EU standards.