What's the difference between dry and wet boiling points?

As brake and clutch fluid is hygroscopic, it will absorb moisture from the air to which it is exposed. This is why the terms ‘dry’ and ‘wet’ boiling points are used.

The ‘dry’ boiling point refers to completely fresh fluid, this level of boiling point is obtained when your brake fluid is consistently changed, keeping the system free from moisture, with a typical water content of below 0.3%.

The ‘wet’ boiling point is relevant to vehicles that do not receive frequent brake fluid changes and therefore the content of moisture absorbed into the fluid is higher.