The metals to be used in your sun shades should, most importantly, be corrosion proof. Ideally, stainless steel is a great fit for sun shades. A mix of alloys and industry-grade plastic can also be used in place of metals.
Metals that are prone to corrosion and rusting should be avoided in sunshades. Any plastic that is not industry-grade or is not powder coated should also be avoided as it can get bleached or broken down easily.
Since sun shades are openly exposed to harsh sun, water, and wind, it is of utmost importance to use a material that is durable.