A soft plastics recycling programme is being rubbished by the Parliamentary Commissioner for the Environment.
The new scheme announced yesterday aims to stop more than four million plastic bags ending up in landfills.
Dr Jan Wright is sceptical it will work.
"You've always got to think about what's the net environmental [impact], you've always got to do the numbers," she told the Paul Henry programme this morning.
"I don't think that just doing things because they sound like a good environmental thing to do, doesn't make them that."