A reusable bubble tea cup sitting on a shelf at a Taipei shop might look like an environmental hero—but only if it actually gets used. Researchers at National Taiwan University have discovered that the feel-good logic of reusability masks a harder truth: a single polypropylene cup must be used at least 120 times to offset the environmental damage created by manufacturing it in the first place.
This finding matters because reusable packaging has become a cornerstone of how cafes, restaurants, and cities hope to reduce waste. But shifting from single-use cups to permanent ones is not automatically better for the planet. It requires reaching a specific threshold that many systems never achieve.
IPCS graduate student Yan-Ruei Huang and Professor Yu-Kai Liao led the research team, which developed a demand-driven life cycle assessment framework—essentially a detailed accounting of every environmental impact from raw material extraction through manufacturing, distribution, use, washing, and eventual disposal. They analyzed real market conditions in Taipei's bubble tea shops, examining when reusable systems actually beat single-use alternatives.
The numbers reveal a surprising inflection point. At 120 reuses, a reusable PP cup breaks even with single-use packaging. But genuine environmental superiority doesn't kick in until a cup reaches 300 uses. Below 120 reuses, manufacturing and disposal account for 75 to 95 percent of the cup's total environmental burden, making a rarely-used reusable cup worse than a disposable one. This is the inconvenient math that undercuts the simple narrative about switching to reusables.
What shifts at higher usage frequencies is revealing. Beyond 100 uses, the environmental burden pivots decisively away from manufacturing toward the operations required to keep a cup circulating—washing and transportation. Electricity now accounts for 40 to 50 percent of environmental impact, while transportation contributes another 35 to 45 percent. At this point, material selection becomes nearly irrelevant. What matters instead is durability, cleaning efficiency, and logistics optimization.
The researchers tested their framework with reusable cup companies operating in Taipei. These businesses confirmed the real-world constraints that the models revealed: cups degrade in appearance, get lost, or suffer physical damage that forces them out of service long before they reach the theoretical reuse threshold. They also noted that environmentally friendly solutions typically require higher investment than current market conditions support.
The finding does not diminish the potential of reusable systems. Instead, it clarifies what genuine sustainability requires. "Reusability alone does not guarantee environmental benefit: usage frequency is the real deciding factor," Huang and Liao concluded. A cup used 300 times can deliver substantial environmental gains compared to 300 single-use alternatives. But that same cup, used only 30 times before being discarded, inflicts more environmental harm than the disposable option ever would.
For cities and businesses aiming to reduce their footprint, the study suggests a clearer path: focus not on owning cups, but on ensuring they actually circulate. The environmental victory is not in the cup itself, but in the systems that keep it moving through hands again and again.