Breathability

Breathability is the ability of a material to allow air and moisture vapor to pass through it. In textiles, breathability describes how easily sweat vapor can move from the skin to the outer surface, helping manage heat and dampness. In building science, breathability refers to a building envelope’s tendency to permit moisture vapor to escape while providing a barrier to liquid water, reducing moisture-related problems.

In textiles, breathability is commonly quantified by moisture vapor transmission rate (MVTR) and by air permeability. MVTR is measured in grams per square meter per day (g/m2/24h); higher values indicate faster vapor transfer. Air permeability measures how easily air passes through fabric, with units such as cm3/(s·cm2) or L/m2/s. Materials with higher breathability tend to be more comfortable but may offer less insulation or wind resistance. Performance depends on temperature, humidity, fabric structure, and movement.

In building materials, breathable membranes allow water vapor to pass while blocking liquid water. Performance is expressed as water vapor permeance (often given in perms or g/m2/day). Breathable assemblies aim to balance vapor transmission with liquid water resistance and adequate air sealing to prevent condensation and mold.

Applications and trade-offs are context-specific. In clothing, high breathability improves comfort during activity, especially in warm or humid conditions, but must be paired with appropriate moisture management and insulation. In buildings, breathable barriers support indoor humidity control and durability, provided interior moisture sources are managed and the overall envelope is correctly designed.

Limitations include that breathability does not guarantee dryness in all conditions; very high activity in wet weather or compromised outer layers can still lead to dampness, and both textiles and building materials require proper layering and assembly to function effectively.