We hired an independent diaper testing lab to evaluate the 15 diapers for the three key performance factors outlined above: how much they absorb, how dry they stay, and how well they prevent leaks.
The lab we commissioned has tested diaper performance on behalf of dozens of manufacturers and brands. The lab has also carried out its own research, with focus groups, babies, and adults, in order to create a rubric for testing, analyzing, and comparing how diapers perform relative to one another and to extrapolate how lab results translate to real-world performance.
All tests used 23 °C, 0.9 percent saline water, which simulates the salinity of urine (the amount of salt in a liquid affects how it is absorbed). We tested size 4 diapers, which typically fit babies weighing between 22 and 37 pounds, and is the most commonly purchased diaper size in the US. We sent 20 samples of each diaper to the lab. Tests were repeated between three and five times to check for variability. The lab tested the diapers’ performance in four areas:
Total absorbency: First, each diaper was submerged in synthetic urine for 10 minutes, and then weighed to see how much it absorbed. The diaper was then spun in a centrifuge for one minute and reweighed. This showed how much liquid the diaper’s absorbent core can retain under force. The lab told us that this second measurement is a good estimate of how much total pee the diaper will hold during normal use.
Speed of absorption: The technician placed a specially sized cylinder onto the topsheet, poured in 120 mL of liquid, and measured how long it took for the diaper to absorb it. (An average 12- to 18-month-old would urinate about 60 mL at a time, so this represents a very heavy wetting—or “insult,” as it’s technically referred to in the lab.) This test shows how quickly the diaper will absorb pee, which is important both to prevent leaking and for the baby’s comfort and skin health. The test was repeated three times.
Surface dryness: After the diaper absorbed the 120 mL of liquid, the technician measured the dryness of the topsheet. The technician placed filter paper on the surface and applied a 2.3-kilogram (about 5-pound) weight, simulating the pressure of a baby sitting on the diaper. The amount of liquid absorbed back into the filter paper models how much moisture the baby will feel when sitting in the wet diaper. This test was repeated three times.
Leak resistance: The technician continuously dripped liquid into the right and left leg cuffs of each diaper and measured how long it took for the liquid to begin seeping out—ideally, the cuffs should prevent liquid from escaping long enough for the pad to absorb the insult.
We compared the testing results with user reviews on sites like Amazon to check if parents’ real-world experiences matched with the lab’s findings. A Wirecutter editor also used some of the diaper brands on her toddler over the course of several weeks.
Almost all the diapers we tested performed very well on certain tests. Every single diaper we tested earned a perfect score on the first dryness test, because they released such minute amounts of liquid back to the surface that the lab told us it would be imperceptible to a baby. In the absorption tests, after spinning in the centrifuge, all diapers held on to at least 240 grams of liquid (about 1 cup), which is about four wettings for a 12- to 18-month-old baby.
We did not test specifically for fit. Babies come in many shapes and sizes, and some diaper designs may fit some babies better than others. All the diapers we tested are adjustable, but some brands have more elastic in the waistband and leg cuffs than others. The width of the back and front panels can also vary, and some diapers have a higher rise than others. When laid flat, most of the diapers we looked at are rectangular, but some brands have a contoured shape, with a roomier waistband and narrower midsection (the part between the baby’s legs). In our research and discussion with other parents, we found that fit is one of the most important factors in preventing poop leakage, aka “blowouts,” but we didn’t find conclusive evidence that any one characteristic—such as stretchier back elastic or a certain cut—works better for all babies.
We also didn’t carry out tests that specifically gauge how well the diapers absorb or hold on to poop; one of the experts at the laboratory told us that they have not yet discovered or designed a testing protocol that satisfactorily evaluates how well a diaper does this. It’s reasonable to assume that no matter how sophisticated and well-performing, no diaper insulates against all poop disasters; the blowout-proof diaper simply does not exist.
