breathable

Breathable describes materials or designs that allow air and moisture in vapor form to pass through, while still resisting liquid water or solid particles in many uses. The term is common in textiles—garments, tents, and footwear—and in building materials such as moisture barriers and house wraps. Breathability aids comfort by reducing heat buildup and removing perspiration.

Breathability is usually assessed in two ways: air permeability, the rate at which air moves through a fabric, and moisture vapor permeability, the rate at which water vapor passes through (often called MVTR or MVP). MVTR is typically reported in grams per square meter per 24 hours (g/m2/24h) and varies widely—from basic fabrics with lower values to high-performance waterproof-breathable fabrics with much higher MVTR. Real-world breathability depends on factors such as temperature, humidity, fabric thickness, and whether the material is dry or saturated with moisture.

Two main mechanisms underlie breathable fabrics. Microporous membranes have tiny pores that block liquid water while allowing vapor to pass. Hydrophilic membranes absorb moisture and diffuse it through the material. Many garments use a breathable membrane layered with an outer shell and a durable water-repellent (DWR) finish to balance breathability with water resistance. In building applications, breathable barriers permit vapor diffusion while helping prevent liquid water ingress and air leakage.

Testing and standards vary by material type. Moisture vapor transmission is commonly measured with standardized tests such as ASTM E96, and air permeability is assessed with other methods. Because results depend on test conditions, manufacturers typically report MVTR and, when relevant, air permeability rather than a single universal value.

Applications and considerations: in clothing, breathability contributes to comfort during activity and affects layering and care. In buildings and outdoor gear, it interacts with climate, layering, and durability. Wetting, compression, and wear can reduce measured breathability over time.