Trash Bag Materials: Check if the compostable trash bag uses natural, biodegradable, plant-based materials. Compostable Trash Bag Certifications: Check if the product is certified and backed by legitimate authorities on compostable and biodegradable materials like the BPI. Compostable Trash Bag Size: Buy the trash bag size that fits your needs - don't settle for one that is too big or too small. Quality: Opt for compostable trash bags proven by other consumers to be durable and leak-proof.