Relative vs. Absolute Humidity

Today we’re going back to high school physics class. Anyone who skipped physics or just didn’t love it, this one’s especially for you. 😉

As we know, air humidity is one of the main factors in how lash adhesive behaves. And there are two kinds of humidity: relative and absolute.

The weight, or more precisely the mass, of water vapor contained in 1 cubic meter of air is called absolute humidity. In other words, it’s the density of water vapor in the air. At a given temperature, air can absorb a very specific amount of water vapor and reach full saturation. Absolute humidity at saturation is called the moisture capacity.

Moisture capacity rises sharply as temperature goes up. The ratio of absolute humidity at a given temperature to the moisture capacity at that same temperature is called relative humidity.

In other words:

At different room temperatures, the % humidity will be different, even though the actual amount of moisture in the air hasn’t changed.

This means it’s more accurate to think about ideal temperature-and-relative-humidity as a specific pairing, not as separate recommended ranges, because at a recommended 70°F versus 75°F the % humidity you need will vary, even while the amount of moisture in the air stays the same.

Dial in your room to the exact pairing your adhesive maker recommends, and use a thermo-hygrometer to keep both readings in check as you work.