Interestingly, all wads used to be biodegradable before the advent of plastic wads.
One hundred years ago, shotgun wads were made from wool felt, cardboard, cork, or fiber. Such biodegradable wads are still used by choice by a small percentage of shotgun users, and as needed in places where plastic wads are banned. Unfortunately, while such wads perform some of the functions of plastic wads (i.e., separating charge from powder, excellent cushioning), they make relatively poor gas seals (causing gas blow-by, unburnt powder, and reduced velocity) and do not protect barrels from steel shot. Lead shot is a cheaper and better shot material than steel (because it is softer and denser), but lead is almost universally banned for waterfowl hunting and may face additional bans in the future.
Accordingly, there is a need for improved biodegradable wads. Many biodegradable (or at least water-soluble) wads have been proposed and developed, but none have really caught on due to a combination of price and performance. CCRM has developed a shotgun wad made from a biodegradable polyhydroxyalkanoate (PHA) plastic, a polymer that is produced naturally by microbes from plant material and is biodegraded into benign components by microbes found in land and aquatic environments. We have incorporated these wads into 12 gauge shotgun shells that outperform some commercial ammunition, providing an environmentally preferable product that gives repeatable, outstanding shot patterns along with acceptable velocities.