Compostable packaging is far from perfect. While it is partly made from plants, it is also made from a petroluem-based compound called PBAT. Petroleum is a non-renewable resource. They also need composting conditions to biodegrade and will not break down unless they have the heat and moisture from a compost. If someone doesn't have a compost and they are sent to landfill, they may produce methane there, depending on the type of landfill it is.