I'm no stranger to period underwear and other "alternative" period products (where my menstrual cup fans at?), so I jumped at the chance to write this guide. When you're on your period, staying dry and comfortable are the top priorities, so I judged every pair of these underwear through that lens.

I first tested all of the above underwear for fit, to determine if they are true to size. That mostly involved a lot of trying them on, wearing them under pants to see how bulky or slim they were and if you could see panty lines.

Next, I tested the absorbency to see if it lived up to the claims. Since it would take me well over a year to test each one of them while on my period, I developed an easily repeatable method in my home lab (also called the kitchen).

I washed each pair of underwear according to the label and air dried. You'll want to wash your period underwear before you wear them for the first time to remove any starch or other chemicals used in the manufacturing process. Air drying is important to preserving the underwear's absorbency -- fabric softener or dryer sheets can leave a film behind that doesn't allow moisture to pass through.

Next, for every pair, I checked how many tampons' worth of fluid they can hold and converted that amount into millimeters. This is not exact because there's some variation in tampons across brands, but in general, one regular tampon can hold 5ml of liquid.

I slowly poured that amount of water over the gusset of the underwear to see how quickly it absorbed and if any water leaked. I left them for 30 minutes and then checked to see how dry they were after absorbing the water. Some were just as wet as when I started the test, others were dry enough to comfortably keep wearing. 

I will caveat that this is not a perfect test. Menstrual fluid usually leaves your body slowly over the course of a few hours, though some people experience short gushes throughout the day. Some of the underwear I tested didn't absorb the entire amount of water right away and/or leaked, but that doesn't mean they wouldn't work for your period. If your flow is steady over the course of a day, period underwear will have time to absorb it slowly, which will minimize leaks.

If you pass multiple clots during your period or experience repeated gushing/flooding, period underwear might struggle to absorb fluid and keep you feeling dry.