Vinyl is measured in weight, so a 15oz. banner is heavier than a 13o. banner, not necessarily thicker. The extra weight doesn't necessarily mean it is alot more durable, but the 15 oz. material is thought to generally be able to withstand wind marginally better than a 13 oz. banner material. The key difference is that the 15oz. material is classified as a blackout vinyl. Blockout Vinyl is opaque, so it won’t let the sun through or be transparent. The 13oz. has good opacity as well, but the 15oz. has better blockout properties. If you are looking for a extra heavy duty vinyl material, we also offer 18oz. vinyl as a custom order. You can find out more about 18oz.