Brake fluids based on glycol ethers are hygroscopic by design. That sounds like a flaw, but it’s what keeps water from pooling at low points in lines and calipers, where it could freeze or flash to steam under hard braking. By absorbing small amounts of moisture and dispersing it, the fluid limits local corrosion and vapor lock. The trade-off is a gradual drop in boiling margin over time, which is why fluid changes matter more than topping up. In Nordic use, vented reservoirs breathe through temperature swings and salted, wet roads, so moisture ingress is steady. The same idea applies when choosing DOT 4: prioritise fresh, sealed fluid and regular replacement.