We carry only the best, 45 mil Fish Safe liner. Manufactured by Pond King, this liner in not made to be roll type roofing material as other liners may be. Roofing liners may leach harmful chemicals into the water killing fish. Pond King liners are tough Rubber liners and can last 40 plus years when covered with stone. Our Underlayment is to be used wherever there may be sharp objects or roots in the ground, which could work there way up to puncture the liner. The underlay is a non-biodegradable 6 Oz. Synthetic woven material that wont degrade and will offer life long protection to the liner system.