On the odd occasion during manufacture, when the base and rim are being welded, very small pieces of material can get stuck in between the inner and outer wall of the Thermal cup base. Over time, and with use, material may become dislodged, causing a slight rattle if the cup is shaken.
A rattle doesn’t necessarily mean the vacuum is compromised, and in most cases the product is entirely fit for use.
We encourage you to continue to use and reuse your Thermal for as long as possible, because even with small imperfections, extending the life of each KeepCup is crucial in lowering its carbon impact.
If you’re finding that your Thermal KeepCup is becoming too hot to hold, there may be an issue with the vacuum - in which case, please let us know.