Breathable Coating
Synthetic polymer coatings with millions of microscopic interconnected voids allow water vapor to escape while blocking liquid water droplets. This microporous polyurethane is applied to high-performance outdoor fabrics to create a breathable barrier against wind and rain. Because the pores are thousands of times smaller than a water droplet but larger than a water vapor molecule, the coating remains waterproof.
Coagulation Method
Wet coagulation of the polymer solution creates the desired cellular structure on the fabric backing. By immersing the coated fabric in a water bath, the solvent is replaced by non-solvent, causing the microporous polyurethane to precipitate. This controlled separation ensures the formation of fine, open pores that are essential for moisture transmission.
Pore Geometry
Inconsistent pore sizes can compromise the waterproofness of the fabric. If the channels are too large, liquid water under pressure penetrates the microporous polyurethane coating, causing leakage during heavy rain.
Performance Tradeoff
Processors must balance the coating thickness with the flexibility of the finished garment. Thick layers of microporous polyurethane offer excellent waterproof ratings but can make the fabric stiff and heavy. Conversely, very thin coatings are soft and highly breathable but suffer from reduced durability and lower resistance to abrasion.
