höyrynläpäisevyys

Höyrynläpäisevyys, known in English as water vapor transmission rate (WVTR) or vapor transmission, refers to the rate at which water vapor permeates through a material. It is a crucial property for many materials, especially those used in packaging, construction, and textiles. The measurement quantifies how easily water vapor can pass through a unit area of a material over a specified period under defined conditions.

This property is typically expressed in grams of water vapor per square meter per 24 hours (g/m²/24h) or in other units depending on the standard and application. A lower WVTR indicates that the material is a better barrier to water vapor, meaning less moisture can pass through it. Conversely, a higher WVTR means the material is more permeable to water vapor.

In packaging, high WVTR materials are used to allow products to "breathe," such as fresh produce, while low WVTR materials are essential for protecting moisture-sensitive products like pharmaceuticals or electronics from humidity. In construction, vapor barriers with low WVTR are used to prevent moisture from entering building envelopes, which can lead to condensation, mold growth, and structural damage. Textiles can also have varying degrees of vapor permeability, impacting their comfort and performance in different weather conditions. Understanding and controlling höyrynläpäisevyys is therefore vital for product performance, longevity, and safety.