Complex sentence: Polyethylene glycol fluids are hygroscopic and will absorb water from the atmosphere, which is necessary to prevent sheer and undiluted water in the braking system, which is very corrosive, also water droplets can freeze in the pipes, thus blocking the system.
Split into simpler sentences: Polyethylene glycol fluids are hygroscopic and will absorb water from the atmosphere, which is necessary to prevent sheer and undiluted water in the braking system, which is very corrosive. Water droplets can also freeze in the pipes, thus blocking the system.