Some brands of tumblers and travel mugs have a lower capacity than is claimed, the Consumer Council said on Wednesday.

The watchdog also found that plastic mugs are not as effective in keeping drinks hot or cold.

The council tested 18 models of tumblers and travel mugs, which claimed a capacity from 350ml to 900ml.

But only four models had the actual capacity that was stated. The rest of them held less liquid than claimed.

Five mugs or tumblers, from Muji, 24Bottles, Decathlon, National Geographic, and PoleBear, were found to have a discrepancy in capacity of more than 10 percent.

“The Council reminds manufacturers that their product design must take into consideration the actual usage by consumers and clearly and accurately state on the product label the actual capacity,” said convenor of the council’s advisory group on digital economy and information technology Jack Poon.

The watchdog also passed the results to the Customs and Excise Department for potential follow up actions.

In the thermal insulation efficacy test, two stainless steel tumblers from NOC and Stanley performed well as they were able to keep the water temperature at over 60 degrees Celsius after six hours.

Thirteen models could maintain the water temperature at above 40 degrees Celsius, but the water temperature in three plastic mugs or tumblers, dropped significantly to between 29 and 26.3 degrees.

For cold drinks with temperatures from five degrees to minus one degree Celsius, temperatures from three plastic models rose to as much as 22 degrees after six hours.

Two-thirds of samples showed a satisfactory performance in the leak-proof test.

The council reminded people to clean their tumblers or mugs as often as they could and recommended they use tools like small brushes to wash narrow bottles.

“It's better for you to clean it thoroughly because you never know when the pathogenic bacteria will breed in your container. So the cleaner it is, the better for your food safety,” the council’s chief executive Gilly Wong said.

“When you buy this kind of tumbler, check out how many parts they have so that you know you have to open it up and how to clean it and put it back, ensure that you know it performs as well as its original,” she said.