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About six years ago, Nike debuted its  construction—yarn wizardry designed to make athletic shoes as comfortable and well-fitting as a knit T-shirt. In July, it unveiled a sports bra with the same technology. After a season of testing, I'm impressed.

The  ($80) looks like your basic pullover racerback. It has almost no seams, to minimize chafing, and a knit “underwire” (basically a strip of thicker fabric) below and between the breasts to provide support and definition. Uniboobs, get out of here. An open weave down the center of the back helps the bra breathe better. 

When I first tested the Fe/Nom this summer, I was immediately struck by the fabric feel: it's unusually silky. This bra fits like a second skin, and it’s definitely softer and conforms better than most sports bras, even the highest-end ones. I’ve now worn it for running and mountain biking, and found it to be perfectly supportive during both. It’s not a squasher/smasher bra—it allows enough space and movement to let me breathe deeply—while also controlling bounce. 

But I'm a C-cup. And Nike's boldest claim about the Fe/Nom is that in size XL, it comfortably supports a 36D. I was initially skeptical. For the past several years, I’ve coordinated sports-bra testing for Runner’s World, and I’ve never heard a D-cup tester endorse a pullover tank. The pullover racerback style tends to be too elastic to adequately support bigger breasts, as it needs to be stretchy enough to get over a wearer's head. 

That said, Nike uses novel construction methods. Flyknit machines create knits with various shapes and properties, which designers can apply with impressive precision. If an athlete needs support here, breathability there, stretch somewhere else, Nike can seamlessly engineer those properties into different parts of the bra. 

I wanted to see if this tech enabled it to solve the support issue, so I gave an XL Fe/Nom to a friend, who wears a 36D. She loved it. “Without underwires or bulky seams, this bra is all comfort from the moment you put it on,” she told me. She ran and did Crossfit workouts in the Fe/Nom, and found it to be just as supportive as the bulkier contraptions she’s used to. 

I should note that when I had another friend (size 36DD) test the XL, she found it to be too bouncy to be comfortable while running. So it seems Nike's right: this bra works for women up to a 36D cup. But I'd love to see it design something for women with even bigger breasts—there are a lot of options for sizes up to 36D out there, and a lot fewer beyond that. 

Other gripes: we all found the shoulder straps to be a touch too long for our torsos. That’s another design limitation with racerbacks—wearers can’t adjust the distance from breasts to shoulders. But Nike says that future versions of the Flyknit bra will be offered in individual band and cup sizes, which should accommodate a wider range of body types. 

Finally, this bra is unusually slow to dry, which surprised me given that open weave in back. Although I didn't notice the bra’s sweat-soaking nature while I was wearing it—it does a good job of wicking moisture away from my skin—the super-slick yarns apparently like to hold onto water. The bra stayed damp for an hour or two after my run. That means it's not a great “trail-to-tavern” bra, but it’s brilliant for workouts that end in a changing room.