Professor of chemistry at the Australian National University Michelle Coote said the bags sold by Coles and Woolworths in response to an ACT Government ban on plastic bags thinner than 35 microns would never really breakdown, but rather just break into smaller and smaller pieces.

''If it's exactly the same plastic, then the thicker it is then the longer it will take to break down,'' she said.

But some Canberrans are using the 15c bags as bin liners. Janeen Williams, of Forrest, said she has not resorted to purchasing bin liners since plastic bags were banned from Canberra supermarkets, but she will have to in the near future.

''I have found the bags on sale for 15c work well as a liner as I have small bins in my apartment,'' Mrs Williams said.

The grandmother and her daughter, Felicity Williams Dowden, who lives in Lyneham, said they both remembered their ''green'' bags most of the time, and Ms Williams Dowden is adamant the ban is a positive step for Canberra.

''It is absolutely a great move - we always carry our recyclable bags now,'' she said.

Almost 600 people responded to a Canberra Times online poll yesterday that asked, ''Have you been buying more bin liners since the plastic bag ban came into effect?''

Just over 65per cent said yes with 34per cent responding no.

About 64 million plastic bags were sent to ACT landfill last year and Professor Coote said Canberrans should switch to biodegradable bags and bin liners.

''[Some bags] are designed to be compostable and in the presence of water will do a process called hydrolysis and turn back into fairly harmless things,'' she said.

But Coles' head of communications, Jon Church said the company had no plans to introduce biodegradable bags in its stores because of the poor quality of materials currently available.

''We believe the reusable bags are a better option for customers to take their shopping home in,'' Mr Church said.

Similarly, a spokeswoman from Woolworths said the company had no plans to introduce biodegradable bags.