It absorbs water.
If your brake fluid is hygroscopic then it means that is will absorb water/moisture from the air and it can effect your boiling point and your brakes may fail at high speeds.
Yes it readily absorbs moisture.
No, oil is not hygroscopic. Oil does not have a tendency to absorb or attract water molecules from its surroundings like hygroscopic substances do.
DOT 5 is silicon based and will not absorb moisture.
Non-Hygroscopic
Hygroscopic refers to a substance's ability to absorb and hold moisture from the surrounding environment. This characteristic makes hygroscopic materials prone to absorbing water vapor from the air, which can lead to changes in their physical properties or chemical reactions.
The hair of the tail of horse is hygroscopic material.
Polyol Ester is also hygroscopic
fluid-balance
Hygroscopic substances are used to absorb humidity.
Potassium hydroxide is hygroscopic and deliquescent.
As far as I know, the PVC is not hygroscopic, it doesn't absorb the moisture. There are several types of PVC though, so there could be some hygroscopic PVC resin, but I haven't encountered it yet. Normally it is dried by hot air driers, which are not suitable for hygroscopic materials, therefore I assume PVC is not hygroscopic...