Does Period Underwear Really Work? We Tested It

Does period underwear really work? Yes, as long as you pick the right absorbency for your flow and change it in time. We didn’t want you to just take our word for it, so we put it to the test. Here’s what happened, including when it might not work for you.

Can period underwear handle a heavy day in white trousers?

Yes. In our test, one heavy flow pair kept white trousers clean for almost 14 hours on a heavy day. Katrīna, a content creator who works with us, did the test herself. She put on a pair of Lola, our mid-rise heavy flow style, at 8:04 in the morning, pulled on white trousers and went about her day. No pad, no tampon and no change of underwear.

At 21:42 she checked. Her white trousers were still completely clean.

That’s almost 14 hours in one pair, which is longer than we’d normally suggest. On your own heavy days, change every 8 to 10 hours, or sooner if it starts to feel full. But it shows how much a heavy flow pair can really handle when the day doesn’t go to plan. You can watch Katrīna’s white trousers test on Instagram.

Yes, she creates content for THATDAY, so you’re welcome to be a little sceptical. That’s exactly why we filmed the whole thing from morning to night.

Can a few pairs get you through a whole period?

Yes. In our test, 4 pairs of period underwear covered one whole period from start to finish, one pair for every kind of day. You can see it in this short reel.

• Lola for the heavy days.
• Katrina and Trina for the regular days, one high-rise and one mid-rise.
• Period-proof thong for the light days at the start and end.

That’s one example, not a rule. For most people, 2 to 3 pairs per cycle is a good start, depending on how long your period lasts and how often you wash them. The trick is matching each day to the right absorbency, which we explain in how to choose period underwear for your flow.

How much can one pair of period underwear hold?

One pair of period underwear holds up to the equivalent of 1 to 6 regular tampons, depending on its absorbency level.

• Light flow holds up to the equivalent of 1 regular tampon.
• Medium flow holds up to the equivalent of 4 regular tampons.
• Heavy flow goes up to the equivalent of 6 regular tampons in the Ella super absorbent period boxers.

Want to see it instead of reading numbers? In this reel we pour liquid onto a pair made for heavy days. It spreads evenly through the absorbent core and takes in about as much as 2 to 4 pads.

Why does period underwear work?

Period underwear works because of its layers. Every THATDAY pair has three.

• A top layer that pulls moisture away from your skin and dries fast, so you feel drier.
• An absorbent core in the middle that takes in your flow.
• A waterproof but breathable outer layer that keeps it all inside and helps hold back odour.

The fabrics are OEKO-TEX certified and every pair is handmade in Latvia. More on that in what period underwear is and how it works, and if you’re wondering about freshness, read is period underwear hygienic.

When might period underwear not work for you?

Period underwear usually doesn’t work when the absorbency is too low, it’s worn too long, the fit is off or it was washed the wrong way.

• The absorbency is too low. A light flow thong on your heaviest day will feel like a mistake. Match the pair to the day.
• It’s worn too long on a heavy day. Katrīna’s 14 hours was a test, not a habit. When a pair feels full, change it.
• The fit is off. Period underwear works best when it sits close to your body without digging in. Check the size chart on the product page, and if you’re between two sizes, go one size up.
• It was washed the wrong way. Fabric softener and tumble dryers can make the layers absorb less over time. Here’s how to wash period underwear the right way.

And on your very heaviest day it’s completely fine to double up with a tampon or menstrual cup. If your flow is on the strong side, have a look at period underwear for heavy flow.

So, does period underwear really work?

Yes, period underwear works. Our tests showed it, with a heavy day in white trousers and a whole period covered by just 4 pairs. Every flow is different, of course, but they show what a well-chosen pair can handle. Pick the right absorbency for each day, find a fit you feel good in, change it when it feels full and look after it in the wash.

Still not sure it’s for you? If you’re new to THATDAY, you can try one pair with our 40-day risk-free trial. If it’s not for you, send it back within 40 days of delivery and get the product price back. Terms apply. Or browse the full THATDAY collection and run your own test.

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