Nonsynthetic brake fluids are hygroscopic, meaning they absorb water—as their moisture content goes up, their boiling point goes down. When the water trapped in the braking system turns to vapor, it creates tiny pockets of compressible gas, reducing efficiency. That's why it's crucial to change and flush brake fluid on a regular basis. Always use new fluid from an unopened bottle so you can be sure it won't be contaminated with water. Most fluid manufacturers recommend against mixing brands and classifications because some chemicals may not be compatible. Before you add anything, check any stickers or warnings on the bike for additional information.