Polypropylene Signs (plastic) are highly recommended for outdoor use. Available in many sizes, polypropylene signs are perfect for safety signs and much more. Polypropylene is UV stable and resists fading and cracking outdoors. Polypropylene is a neutral plastic containing only 2 elements Carbon and Hydrogen. Polypropylene is an extremely heat tolerant and stable plastic making it a suitable alternative in all climates around the country. Polypropylene is 100% recyclable. Request a quote today.