237sj, choose carefully if you want genuinely usefully biodegradeable. The earth rated bags are not. They break down into smaller pieces of plastic but it stays plastic. Additionally such material is not storeable. Unless you are going to bury the used bags yourself (and dog poo does not compost or rot down easily) then it won't be treated as compostable material by your local council. If the council uses landfill sites then it may help a miniscule amount but if they are going to be close system burned anyway then you may be spending money to no advantage.