No, dot 5 will not absorb moisture. I've had it in my olds for over 40 years. Sometimes the car sits for years un used. I live in an area where it can get very humid in the summer. I have never had an issue with anything in the brake system rusting, seizing, leaking, or any other type of failure. I pulled the car out of 23 years of storage, and the brakes were still fine.