- A new study published in Journal of Hazardous Materials: Plastics found that to-go coffee cups can shed significant amounts of microplastics, especially when exposed to heat.
- Researchers discovered that fully plastic polyethylene (PE) cups released the most microplastics, while paper cups coated with PE shed far fewer particles.
- The research highlights temperature and surface texture as key factors in microplastic shedding, offering new insight into everyday plastic exposure.
According to 2024 data from the National Coffee Association, daily coffee consumption in the U.S. is at an all-time high, with some 67% of people saying they’ve sipped their favorite brew within the last day. While most people make it at home, 35% of those coffee drinkers had their coffee prepared “away from home,” meaning many picked it up at a coffee shop. While daily coffee consumption offers numerous benefits, one recent study is drawing attention to a byproduct of getting coffee to-go. It may even prompt you to start bringing your own reusable mug more often.
In February, researchers published the findings of their new study in the Journal of Hazardous Materials: Plastics, which examined how and when beverage containers, including to-go coffee cups, shed the most microplastics, those teeny, tiny particles getting a lot of attention for their potential impact on human and environmental health. And it turns out that heat matters in the equation.
To understand the microplastic problem, the team first conducted a meta-analysis, synthesizing findings from dozens of studies, focusing on papers that examined how microplastics are released at different water temperatures. They then normalized the results across all studies to compare temperature effects.
Next, they conducted their own case study, collecting beverage cups commonly used in cafes and shops across Brisbane, Australia, and selected two cup types for testing: polyethylene (PE) plastic cups and paper cups coated with PE (the plastic lining that makes paper cups leak-proof).
They then measured the amount of microplastics shed by filling each with water at different temperatures, including 41°F for cold drinks and 140°F for hot drinks.
The researchers found that, across the studies they collected, microplastic release increased with temperature, and they confirmed this in their own case study. Specifically, they found that although both cup types released microplastics, the PE cups released the most, even under cooler conditions. The paper cups coated in PE also released microplastics, but far fewer than their fully plastic counterparts. In fact, when the team moved from cold to warm water, microplastic levels in PE cups increased by 38.4%, whereas only 3.3% increased in PE-coated paper cups.
As for why that may be the case, the researchers said it may come down to texture, with the PE cups having a “rougher” inner surface, which likely makes them more prone to shedding.
So, to minimize microplastics exposure, it’s best to avoid these to-go mugs altogether and invest in reusable ones. As an added perk, many coffee shops, including Starbucks, offer discounts to customers who bring their own mugs, making it a win-win.
How to tell if your to-go cup is plastic-lined
Most paper coffee cups aren’t actually paper all the way through. To prevent hot drinks from soaking through, they’re typically lined with a thin coating — often plastic, but not always. Here’s how to tell what kind of cup you’re drinking from:
- Do the tear test: If you gently tear a used cup and notice a thin, shiny film separating from the paper, it’s likely plastic-lined.
- Check the texture inside: Plastic-lined cups often feel slick or waxy, whereas non-plastic linings feel more matte or fibrous.
- Look for recycling clues: Cups labeled “not recyclable” or that require special recycling or composting programs often have a lining — whether petroleum-based plastic or a plant-based alternative — that can’t be processed through standard curbside recycling.
What lines paper cups when they’re not plastic? Some cups feature plant-based coatings, primarily PLA (polylactic acid), a bioplastic derived from fermented plant starches such as corn or sugarcane. Others may use water-based or mineral coatings to create a moisture barrier without relying on conventional plastics. These options are often found on cups labeled compostable or plastic-free, though proper composting typically requires commercial composting facilities.
