New research shows that single-use cups, hot or cold, sheds microplastics into our drinks. We wanted to understand the science, and share it with you.
To-go cups are so super convenient, but there has been mixed messaging of the safety of these cups - on both its effect on our planet, and its impact on our consumed beverages. Recent years have rolled out compostable options for these cups to address the first issue – a more earth-friendly solution. However, most of these still end up in landfill, and the PLA generally needs high-end composting facilities to break them down properly, which most Americans don’t have access to.
The second issue hasn’t been talked about as much, the impact of that plastic-lined or fully plastic cup on the beverage inside. A wave of peer-reviewed studies, including a comprehensive 2025 analysis out of the University of Birmingham, now confirms what researchers have suspected for years: every type of disposable cup — paper-lined, polystyrene, polypropylene — releases microplastics into beverages. And no temperature is safe.
Hot drinks are worse — but cold isn't safe either
Temperature is the key variable. A 2024 study published in Foods tested cups at 4°C, 50°C, and 80°C and found that microplastic release climbed sharply with heat — particles released at warm and hot temperatures were significantly higher than at cold temperatures. The University of Birmingham team then put real-world beverages under the microscope, buying drinks from major UK retailers and coffee chains between August and December 2024.
Hot tea clocked in at 60 MPs per liter on average — nearly double the count of iced tea at 31 MPs/L. Hot coffee averaged 43 MPs/L compared to 37 MPs/L for iced. The cold drinks still showed contamination. The difference is a matter of degree, not kind.
"Not a single beverage tested — across 155 samples — was free from microplastic contamination."
The particles found ranged in size from 10 to 157 micrometers. Fragments were the most common shape, followed by fibres. The main culprits were polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyethylene (PE) — all are everyday materials that coat paper cup linings or make up plastic cups entirely.
It's not just about the plastic particles
A separate 2024 study published in LabMed Discovery found that beyond the particles themselves, hot liquid contact causes the lining to release phthalates, which are heavy metals including lead, chromium, and nickel, and endocrine disruptors like styrene and vinyl chloride — all within the first 20 minutes of contact. These compounds are linked to hormonal disruption, oxidative stress, and inflammation.
The research community is still working to establish recommended thresholds for microplastic ingestion in humans, but the evidence is clear that these particles cross biological barriers, accumulate in tissue, and carry chemical payloads.
The "paper cup" myth
Many people reach for the paper cup thinking it's the environmentally sound choice, or at least the less plastic-y one. The research suggests otherwise. Paper cups are lined with a thin film of polyethylene — that's what makes them waterproof — and it's precisely that lining that sheds particles into your drink. The 2024 Turkish study found microplastic counts ranging from 126 to 1,420 particles per liter across cup types, with PE-coated paper cups showing the lowest baseline counts at cold temperatures but still contributing meaningfully at hot brew temperatures.
Polystyrene cups (styrofoam) showed the highest microplastic release of any material tested, significantly outpacing PP, PE, and EPS cups. If you're still drinking from one of those, it's worth knowing that.
What this means for your daily ritual
The average coffee drinker gets a to-go beverage multiple times a week. If every hot coffee from a paper to-go cup delivers 43+ MPs/L, and you're drinking 12 ounces, you're taking in dozens of plastic particles per cup — before accounting for whatever's already in the water or milk. This is the everyday exposure that previous research has historically undercounted, because most studies have focused only on water.
The good news is that this is one of the more actionable exposures in our lives. Unlike microplastics in the ocean, or in the air we breathe, what cup we choose is something we control every single day.
Make the switch: what actually helps
 |
Carry a stainless steel or glass travel mug |
 |
If you forget your reusable cup, ask for an in-house cup rather than disposable |
 |
Brew at home in glass, ceramic, or stainless steel — and if you use a subscription like our Zero-Waste Coffee Club, your packaging is also plastic-free! |
 |
Avoid microwaving or pouring boiling water into plastic-lined containers — heat accelerates every form of leaching |
At Swelter, we think about the full lifecycle of every coffee we roast — from the soil it grew in, tended by the women farmers we source from, to the cup you hold in your hands. Choosing reusable isn't just an environmental decision, it's a personal health decision too!
One of our fav reusable cups is the MiiR tumbler. It fits well in the hand, and in most cupholders (car and bike!). We also like the glass Keeper Cup — this is great for you if you don't like the stainless steel "taste" (which we don't!).
Would you like a Swelter branded travel mug?(with a super cute illustration or pattern?) Let us know! Send us an email hello@sweltercoffee.com
______
Sources
Akbulut et al. "Microplastic Release from Single-Use Plastic Beverage Cups." Foods, 2024. · University of Birmingham / Alqahtani et al. "Synthetic microplastics in hot and cold beverages from the UK market." Science of the Total Environment, 2025. · LabMed Discovery, 2024 (via EurekAlert). "Microplastics associated contaminants from disposable paper cups."
