From July 1, Queensland and Western Australia will ban single-use, lightweight plastic bags from major retailers, bringing the states into line with the ACT, South Australia and Tasmania.

Victoria is set to follow, having announced plans in October 2017 to phase out most lightweight plastic bags this year, leaving only New South Wales without a proposed ban.

Supermarkets have followed suit.

There's also a growing grassroots movement to ban plastic straws, with nearly 100 venues Australia-wide already having phased out single-use straws through partnerships with The Last Straw campaign.

So, what do plastic bans actually mean and are they truly better for the environment?

Heavy-duty plastic bags potentially worse for environment?

Plastic bags found inside a dead sperm whale that washed up in Spain. ( Twitter: Espacios Naturales Murcia )

The ban on plastic bags only relates to single-use plastics thinner than 35 microns or 0.035 millimetres (human hair ranges from about 60 to 120 microns).

These are typically known as high-density polyethylene bags or HDPE bags.

Woolworths currently gives out more than 3.2 billion single-use HDPE plastic bags every year, and according to a 2009 study, about 1 per cent of those, or 30 to 40 million, find their way into the environment.

But thicker, more durable plastic bags will still be available to purchase in most supermarkets.

So is this any better for the environment? The short answer is, it depends.

If consumers continue to use heavy-duty plastic bags at the same rate as lightweight bags, it can actually be worse.

A UK Government life-cycle analysis of single-use versus reusable bags reported that heavy-duty plastic bags (low-density polyethylene or LDPE bags) need to be reused at least four times to make up for the increased greenhouse gas emissions caused by their production, when compared to single-use HDPE bags.

And heavy-duty plastics may also take longer to break down in the environment, though both will eventually end up as harmful microplastics if they enter the ocean.

Professor Sami Kara from the University of New South Wales said introducing heavy-duty reusable bags is a short-term solution at best.

"I think it's a better solution but the question is, is it good enough? To me it's not good enough.

"It's better in the long term that we don't use [plastic bags] at all."

Do lightweight-bag bans reduce the amount of plastic we use?

"Barrier bags" will still be available at supermarkets. ( ABC News )

Concerns that heavy-duty plastic bags are being discarded after a single use prompted ACT Climate Minister Shane Rattenbury to order a review of the scheme in the ACT earlier this year, citing "perverse" environmental outcomes.

Still, Keep Australia Beautiful's national report for 2016-17 found a drop in plastic bag litter after plastic bag bans came into effect, particularly in Tasmania and the ACT.

And a review of the ACT's bag ban in 2014 found annual plastic bag waste had dropped from 266 tonnes to 171 tonnes after it was implemented.

But these short-term gains may be wiped out by population growth, meaning we'll end up with more people consuming more energy-intensive bags in the near future, Dr Kara warned.

"When you look at the population increase predicted by the UN by 2050, we're talking about 11 billion people in the world," he said.

"We are talking about 4 billion extra people, and if they all use the heavier plastic bags, they'll eventually end up in landfill."

The other issue is that shoppers may become accustomed to buying plastic bags, rather than changing their behaviour long term.

Ireland reported a 90 per cent reduction in single-use bags after introducing a 15p (22c) levy in 2002.

In 2007, the price was bumped up to 22 euro cents (32c) after people returned to their old habits.

What are the better options?

Green bags are a much more sustainable option than single-use plastics.

There are different energy costs for all bag materials, but the best way to reduce the impact of our bags is to reuse them.

Cotton bags are water and energy-intensive to produce. Estimates suggest they need to be used around 130 times to achieve a reduction in greenhouse gases.

But they are generally able to hold more items and can be used repeatedly. And they biodegrade, rather than breaking down into harmful pollutants.

Dr Kara said reusable bags made from materials like cotton are the only real solution.

"That's the way we used to do it. I remember my grandmother, she used to make her bags from leftover fabric," he said.

"Instead of wasting old fabric she'd give it a second life. That's the mindset we need to be shifting to."

A Zero Waste report prepared for the South Australian Government in 2007 found that reusable, polypropylene green bags — the sturdy shopping bags sold at most supermarkets — achieved the greatest environmental benefits when used multiple times compared to alternatives like paper or calico bags.

They estimated that if every Australian household switched to green bags, 2,200 garbage trucks would be diverted from landfill annually, 42,000 tonnes of greenhouse gases could be abated, and 50,000 litres of water saved.

The Last Straw?

Venues around Australia have been signing up to The Last Straw. ( Supplied: Harriet Spark )

In Australia, efforts to get rid of single-use plastic straws have been piecemeal, but momentum is growing.

So far, around 100 venues, including bars, restaurants and clubs, have partnered with The Last Straw campaign to remove all single-use straws.

In January, more than 30 tourism operators in Cairns and Port Douglas signed up to ban plastic straws at businesses around the Great Barrier Reef.

And earlier this month, 10-year-old Molly Steer convinced the Cairns Regional Council to get rid of straws and other single-use plastics in its council operations.

But Australia is likely to lag behind other countries when it comes to a nationwide straw ban.

Scotland has announced plans to phase out straws by 2019, and there are rumours of a European Union-wide ban after a Twitter spat between UK Environment Minister Michael Gove and European commission vice-president Frans Timmermans in February.

After Mr Gove tweeted on the subject of a UK straw ban, Mr Timmermans responded that the EU is "One step ahead of you. EU legislation on single-use plastics coming before summer".

Straws typically aren't able to be sorted at mechanical recycling facilities, and end up as landfill.

They also have an uncanny ability to find their way into the environment, where they are eaten by seabirds, turtles and other marine life.

Volunteers in Sydney have so far pulled more than one thousand single-use straws from Manly Cove, where local dive instructor Harriet Spark has launched "Operation Straw" in an attempt to clean up the mess.

"On one of our dives we actually found an octopus holding four straws in its tentacles," she told ABC Radio Sydney earlier this year.