If you could take a tour of UL, you would find lots of laboratories with scientists in white coats carrying out tests of all kinds. On that tour, if you were to walk into the sensory lab at UL’s consumer testing facility in Canton, Mass., you would find technicians conducting sniff tests of diapers sealed inside of glass jars.

“Manufacturers want to know how well their brand of diaper performs compared to the competitors,” said Melissa Lohnes, lab manager, in an article for Inside UL. “The goal for the client is that the intensity of smell will decrease over time.”

The performance, including smells, of these products is an important consideration for consumers, who buy more than 73 million disposable baby diapers in the U.S. every year.

According to Inside UL, the diaper sniff tests work like this:

A lab technician places synthetic urine on the inside of the diaper inside a jar using a glass flask and funnel. Scientists call this “insulting the diaper.”

The diaper then sits in a glass cookie jar for a set amount of time, usually two to eight hours, with the mixture absorbed into the absorbent core gel portion of the diaper that wicks away the liquid and keeps a baby dry even when the diaper is wet.

Then the samples are moved to the lab’s sensory panel room for the next portion of the test: judging. Five judges enter, moving to his or her assigned spot, and the UL manager starts the test. Each judge lifts a jar’s lid, sniffs once or twice, closes the jar and notes the rating before moving onto the next sample. After the judging, technicians use each sample’s assessments to score each diaper.

According to Lohnes, the lab’s testing rates at a 95 percent confidence level, meaning that if they rerun the test, the technicians would get the same results 95 percent of the time.

See the test in action in this video.

This type of sophisticated sniff test can be performed on many products where scent matters, from pet housebreaking pads to incontinence products for adults. This way manufacturers can find out how their products fare in a scent contest, and make adjustments, providing consumers with what they want.