... Model Number: 20,25,47,58 mm Style: silica gel circ silica circle for solar water heaterProducts feature1,made of 100% silicone material ... have good quality and a long service life.Product attributesNamesilica gel circleFull specifications20,25,32,47,58,70mmProduct size20,25, ... life10--15 yearsCustomizedUnilateral or bilateral according to your requirements silica gel circle for solar water heater