Long before the first ThirdLove bra was made, our founder Heidi Zak started talking to women—and asking lots of personal questions—to find out about their bras.

Wireless or wire? Push-up or lightly lined? How much coverage? While opinions varied, some clear patterns emerged. First, there were surprisingly few rave reviews about bras. The vast majority of bras were, according to women, “fine” or “just ok”—nothing to write home about. Second, most bras were uncomfortable, and no matter their size, women struggled with a range of fit issues from slipping straps to overflowing cups.

How was it possible for so many different bras to be failing so many different women? Why didn’t more women love their bras? The answer, it turns out, lies in how most bra sizes are made.

Here’s how conventional bra sizing works: companies use a size 34B fit model, adjust the bra to fit her, then make larger and smaller versions for other sizes. So whether you’re an A cup or a G cup, chances are you’re wearing a version of a B cup that’s just been scaled up or down.

Once you know that, then it’s not surprising that most bras don’t fit well. The conventional way of sizing using fit models doesn’t account for real variations like sloping shoulders, long torsos, and a whole range of breast shapes. Women’s bodies aren’t simply carbon copies of each other in smaller and larger sizes, so why should their bras be?

Starting early on, Heidi and the ThirdLove team realized that in order to make bras for real women, they needed to fit them to real women—not fit models. (After all, how many women do you know who look like a typical lingerie model?)

To this day, we still fit and test our bras on a range of different women in every size we produce, including our own employees, friends, and most importantly—our customers. Customer feedback is hugely important in the development of our bras.

While fitting ThirdLove bras to real women is important to us on principle alone, it also helps us discover the fit details that make our bras supremely comfortable. Our design team specifically looks for issues that might occur with one size but not another; like when creating our plunge bras, they realized the strap placement needed to be adjusted on larger cup sizes to keep them from digging into women’s shoulders.

Perhaps most significantly, fitting bras to real women is what helped us realize that over a third of all women are actually in-between bra sizes. That insight led us to create our signature half-cup sizes, a revolution in the bra industry.

We’ve always believed that the little details make a big difference: an adjustment here or a tweak there can make for a far more comfortable bra. Fitting bras to real women, rather than fit models, is one way we bring that belief to life. We’re mindful of the details that make each woman unique, and design bras to celebrate those details.