4mm thick (about 1/6") opaque white corrugated plastic. This product is weatherproof and fluted for ease of mounting on steel or plastic stakes. Printed with OEM brand National UV's premium POP+ UV-cured glossy inks for long life and rich opacity. This product is affordable, recyclable and extremely versatile for a wide variety of marketing opportunities. This is the best product for easy readability in direct sunlight. Sunlight does not shine through. If the second side is printed, the ink color from the other side is not readable from the opposite side. Always follow local yard sign display regulations.