Madbull biodegradable BBs are made from Polylactic Acid, a thermoplastic aliphatic polyester derived from completely renewable resources such as Corn, Tapioca and even Sugar Cane. So not only are these BBs completely biodegradable but they are also completely disconnected with the petrol chemical sciences (oil).
As a thermoplastic, heating up the pellets will cause them to melt again but with a melting point of somewhere around 50-80 degrees Centigrade / 122-176 Fahrenheit this is incredibly unlikely to happen (unless you have a habit of baking your ammo in an oven). If you are still worried, this plastic is also used in microwavable plastic trays, disposable hot drink cups and diapers so really your BBs are nice and fine.
The highly agile nature with which PLA can be manipulated during manufacturing means the BB forming process can be very precise. These BBs are around 5.95mm with a +/- 0.01mm tolerance and weigh 0.28g, very nice stats for high precision ammo used in high end weapons and long range platforms like sniper rifles and marksman weapons.
This is a 3000 round carton which is quite normal for a BB package and as it is a rigid and squared shape you can more easily store such cartons on a shelf, in a box or bag as they will sit and stack much more easily then a soft bag. Also, the carton forms a spout when open so pouring out BBs is a much more precise affair.
Madbull went ahead one step further and actually serves these BBs in a cardboard milk-carton style package which makes the entire thing completely disposable and biodegradable.