This article is republished from The Conversation (January 14, 2026 12.26pm AEDT)

It’s 7:45am. You grab a takeaway coffee from your local cafe, wrap your hands around the warm cup, take a sip, and head to the office.

To most of us, that cup feels harmless – just a convenient tool for caffeine delivery. However, if that cup is made of plastic, or has a thin plastic lining, there is a high chance it’s shedding thousands of tiny plastic fragments directly into your drink.

In Australia alone, we use a staggering 1.45 billion single-use hot beverage cups every year, along with roughly 890 million plastic lids. Globally, that number swells to an estimated 500 billion cups annually.

In new research I co-authored, published in Journal of Hazardous Materials: Plastics, we looked at how these cups behave when they get hot.

The message is clear: heat is a primary driver of microplastic release, and the material of your cup matters more than you might think.

What are microplastics?

Microplastics are fragments of plastic ranging from about 1 micrometre to 5 millimetres in size – roughly from a speck of dust to the size of a sesame seed.

They can be created when larger plastic items break down, or they can be released directly from products during normal use. These particles end up in our environment, our food, and eventually, our bodies.

Currently, we don’t have conclusive evidence on just how much of that microplastic remains in our bodies. Studies on this subject are highly prone to contamination and it’s really difficult to accurately measure the levels of such tiny particles in human tissue.

Furthermore, scientists are still piecing together what microplastics might mean for human health in the long term. More research is urgently needed, but in the meantime, it’s good to be aware of potential microplastic sources in our daily lives.

Temperature matters

My colleagues and I first conducted a meta-analysis – a statistical synthesis of existing research – analysing data from 30 peer-reviewed studies.

We looked at how common plastics such as polyethylene and polypropylene behave under different conditions. One factor stood out above all others: temperature.

As the temperature of the liquid inside a container increases, the release of microplastics generally increases too. In the studies we reviewed, reported releases ranged from a few hundred particles to more than 8 million particles per litre, depending on the material and study design.

Interestingly, “soaking time” – how long the drink sits in the cup – was not a consistent driver. This suggests that leaving our drink in a plastic cup for a long time isn’t as important as the initial temperature of the liquid when it first hits the plastic.

Testing 400 coffee cups

To see how this works in the real world, we collected 400 coffee cups of two major types around Brisbane: plastic cups made of polyethylene and plastic-lined paper cups which look like paper but have a thin plastic coating inside.

We tested them at 5°C (iced coffee temperature) and 60°C (hot coffee temperature). While both types released microplastics, the results revealed two major trends.

First, material matters. The paper cups with plastic linings released fewer microplastics than the all-plastic cups at both temperatures.

Second, heat triggers a significant release. For the all-plastic cups, switching from cold to hot water increased the microplastic release by about 33%. If someone drinks 300 millilitres of coffee in a cup made of polyethylene per day, they could ingest 363,000 pieces of microplastic particles every year.

But why exactly does heat matter so much?

Using high-resolution imaging, we examined the inner walls of these cups and found that all-plastic cups had much rougher surfaces – full of “peaks and valleys” – compared to the plastic-lined paper cups.

This rougher texture makes it easier for particles to break away. Heat accelerates this process by softening the plastic and causing it to expand and contract, creating more surface irregularities that eventually fragment into our drink.

Managing risks

We don’t have to give up our morning takeaway habit, but we can change how we approach it to manage the risk.

For hot drinks, the best option is to use a reusable cup made of stainless steel, ceramic, or glass, as these materials do not shed microplastics. If we must use a disposable cup, our research suggests that plastic-lined paper cups generally shed fewer particles than pure plastic cups, though neither is microplastic free.

Finally, since heat is the factor that triggers plastic release, avoid putting boiling liquids directly into plastic-lined containers. Telling the barista to make our coffee slightly cooler before it hits the cup can reduce the physical stress on the plastic lining and lower the overall exposure.

By understanding how heat and material choice interact, we can design better products and make better choices for our daily caffeine fix.

Author

Dr Xiangyu Liu
Researcher, Solving Plastic Waste CRC
Research Fellow, Griffith University

Griffith University is a research partner of Solving Plastic Waste CRC.

Dr Xiangyu Liu acknowledges the contribution of Distinguished Professor Chengrong Chen, Research Director, SPW CRC and Distinguished Professor Andy Ball, Program Leader, SPW CRC, to this article. This article is republished from The Conversation.

The Solving Plastic Waste CRC (SPW CRC) brought together its Partners from across Australia for its inaugural Annual Partners Event, held in Melbourne from 21–23 October 2025. The three-day program connected industry, government, not-for-profit and research Partners, marking the first major gathering since SPW CRC’s establishment and launch event in 2024.

On 21 October, the event series began with the Industry Researcher Development Day, where SPW CRC PhD and post-doctoral researchers built their skills in communication, leadership and innovation management. Facilitated by Associate Professor Brian McIntosh, Deb Friel, and industry experts, the day focused on strengthening connections among SPW CRC’s next generation of industry researchers.

On 22 October, more than 90 attendees joined the Annual Partners Conference at CSIRO Clayton to learn about research initiatives within SPW CRC’s four research programs and what’s next. The day opened with a Welcome from Dr Leonie Walsh, Chair of the SPW CRC Board, followed by Dr Ian Dagley, CEO, outlining SPW CRC’s progress to date, and Distinguished Professor Chengrong Chen, Research Director, providing an overview of the four research programs, their projects, and the Education & Training Program.

The Research Program Leaders then introduced their areas of focus, inviting Project Leaders and Partners to share their project goals and early-stage work. Each research program also featured a lively panel discussion and Q&A, with audience members actively engaging and sharing perspectives from across the plastics value chain.

Just 15 months into SPW CRC’s journey, the day offered a valuable opportunity to showcase the breadth of projects underway and strengthen connections across the network. The energy in the room reflected the enthusiasm and collaboration at the heart of SPW CRC.

The keynote presentation by Dr Deborah Lau, Research Director, Industry Environments, CSIRO, titled Plastic Waste in Australia: Current Landscape and Future Research Directions, reinforced the importance of cross-sector partnerships in accelerating solutions to plastic waste.

The SPW CRC Education & Training Program was also presented, highlighting the organisation’s commitment to building capability through its hands-on Industry Doctoral Program and the first Microcredential Program of its kind within a CRC.

The day concluded with the Annual Partners Dinner, where Dr Ian Christensen, CEO of iMove CRC, delivered a keynote address titled ‘Off and Running’ – Some Things to Think About When Establishing a New CRC. The evening provided an opportunity for all attendees to connect, share experiences and build momentum for the collaborative work ahead.

The event closed on 23 October with specialised workshops on IP, Patents and Commercialisation, delivered by experts from Davies Collison Cave and Elementary Law. These sessions explored the patent landscape in polymer recycling, the value of IP protection for early-stage ventures and practical approaches to commercialising SPW CRC research outcomes.

We extend our warmest thanks to all Partners and attendees for being part of our first Annual Partners Event. We look forward to reconnecting at upcoming networking events and to reconvening at next year’s event to share progress, strengthen collaboration and continue building a lasting legacy for Australia’s circular economy for plastics.

The Ending Plastic Waste Symposium 2024, led by CSIRO in partnership with RMIT University as host of the ARC TREMS Hub was held on Tuesday 6th August and Wednesday 7th August at Sofitel Melbourne on Collins. The symposium showcased the latest science and technology research across the plastic waste ecosystem with experts from research, industry, and government discussing cutting-edge solutions to end plastic waste.
Key topics presented included plastic design and materials, advances in recycling and resource recovery, plastic in the environment, circular economy and system perspectives and international approaches.

The event provided a valuable opportunity for experts from industry, research and academia to foster connections and future partnerships. Sustainability efforts as part of this event included avoidance of single-use plastics, encouraging the use of reusable items, and included a 50% vegetarian dinner to reduce the carbon footprint.
To view highlights and access presentations and a highlight video from the event visit CSIRO Ending Plastic Waste Symposium 2024.