Flex Magnets Flex magnets come in two sizes: 3.5 x 5 and 2.5 x 3.5 inches. They have rounded corners and a matte finish. The strong magnet will not allow it to slip on the refrigerator door. They are flexible, so they can conform to somewhat curved surfaces. They should have at least 480x350 pixels. Color reproduction is impressive, but not quite as accurate as photographic prints.