The Physics of Bras | Hacker News Reader

The Physics of Bras

discovermagazine.com

61 pointschaostheory31 comments

What follows are the musings of an ex-lingerie designer.

Side note: Humans, btw, are the only animals that sport full breasts all through their youth. Most mammals, including all simians and apes, only sport enlarged breasts when feeding their young.

Simplistically, cup-size is the chest-to-breast ratio, designed to compensate for the fact that radius of the cup is almost, but not entirely, independent of the chest circumference. It does not have a strong correlation to volume of the cup or to mass, although acute cup-sizes are more common at larger chest sizes.

Human bodies grow very disproportionately at either extreme of size. For example, height is a very poor indicator of girth, although it bears a small correlation, and vice versa. Similarly, larger women have a higher incidence of acute cup-sizes, but the shape, consistency and mass of the breasts are very different from what you'd expect through linear scaling.

Ultimately, larger women are a different market. It's common for a larger woman to have large breasts that have a small footprint on her torso. Most lingerie does not account for this. Most lingerie is also not built to bear the weight/consistency of larger breasts. You need to use load-distributing design, as well as resilient/soft materials to ease the stress on the back. And then, you have to put the whole thing together into a sexy package. It almost make it more fun to write code :)

Wondering if this upvoted article will generate any serious discussion. I stopped counting after I had gone through 9 different bra sizes over the years. I found the article quite interesting.

Do you have any idea what caused this? I have yet to met someone with such a huge variation, except mothers who are breast feeding, but that's another thing and it's expected.

I'm not sure why that's a surprise, I'd be surprised if a woman didn't have a wide variation of sizes to choose from. Not only are "standard" bra sizes not entirely the same across manufacturers, but also there are all sorts of different types of bras out there to get different looks. And that's not even considering how physically different breasts can get, even for a specific woman depending on the day.

Having two babies, being put on steroids for health problems, weight gain and loss, and living at 3000 feet above sea level for 2 1/2 years which caused my lung capacity to increase and thus my ribcage to enlarge. This permanently changed the number part of my bra size (and probably saved my life the last time I had pneumonia and was bedridden, so it's all good). Cup size is a relative thing, dependent in part on that first number. The short version: The number part of it is a reference to the measurement around the rib cage directly below the breasts and the cup part tells you how many inches larger than that the measure around the fullest part of the breast is. An "A" cup is one inch. A "B" cup is 2 inches. Etc. Though the number part is a not a direct measure of the ribcage - ie a size 36 bra does not equal a measure of 36 inches around the ribcage. To make this arcane art of bra sizes even more unfathomable, they add a different number to the basic measure depending upon whether it is above or below a certain size -- and I no longer remember what the size cut-off is or what the different numbers are that they add.

I remember in one of my materials classes they used bras as an example where martensitic metals were used. Apparently these materials were chosen to help bras retain their shape (such alloys are also called shape-memory alloys). However, shape memory alloys usually deform back once heated. I've always wondered if this was true. Anyone who has ever washed theirs in hot water want to confirm?

Generally speaking, it's a bad idea to toss bras in a washer and dryer on high heat. Ideally, they should be hand-washed. If that's too much hassle, one should at least put them in mesh lingerie bag so the straps don't get all tangled up with parts of the washer and other clothes, which tends to deform the straps. The hooks of a bra can also get caught on other clothing and damage the other clothing. Washing bras in hot water generally shortens their lifespan. A good bra can be quite pricey so some women who hand-wash nothing else do hand-wash their bras, especially if they are hard to fit.

There is definitely an under-served niche here. From my conversations with other busty women, most bras and swimwear are either un-fashionable or ill-fitting, or un-supportive.

I recently decided I would learn to sew my own swimwear and bras since most of what fits me is horribly ugly and overpriced... I'm in my 20's, fit/5'8"/narrow ribcage/large cups. Forget about factoring support into the equation.

After 10 years of spending hours and hours every spring/summer looking for the perfect fitting bikini, I realized that in that same amount of time, I could learn how to make my own swimwear and be set for the rest of my life. "give a man fish he's fed for a day, teach him to fish he's fed for life"

Going through bra and swimwear patterns, I've learned that the construction ranges from simple to very complicated. Unfortunately, nobody in the industry appears to be doing anything that's particularly interesting or ground-breaking. Very little that appears to be designed by and for a large-busted woman. Patterns are classic, even corsetry-inspired. No new construction methods or materials. Too bad because there is a huge market for supportive and attractive bras - "of the future"?

Lululemon has some great sports bras that are very supportive and cute and the price is reasonable. I wish more companies would follow suit.

What I'd really love is supportive bras with moisture-wicking materials covering the underwire. I have no idea why no companies that I know of, other than Lululemon, have capitalized on this. It's so obvious to me!

holy mother of "A pair of D-cup breasts weighs between 15 and 23 pounds—the equivalent of carrying around two small turkeys."

Yup. It causes lots of back pain.

That statistic seems slightly off to me.

If we assume that the breasts are the same density as water (which is probably too high, as they're mostly fat, which is less dense than water), 23 pounds is about equal to a 12 inch by 7.5 inch by 7.5 inch block of pure flesh.

Maybe it's just me, but I think that fails a simple sanity test.

Edit: Wikipedia says "The average breast weighs about 0.5 kilograms (1.1 lb)" with some decent sources, and given that the average bust is a C-cup, I highly doubt that a D-cup weighs 5-10 times more than that.

"D-cup" also isn't enough information to gauge volume. A 36-D is larger than a 34-D. And remember that volume (and hence mass) increases as the cube of length, so two inches more in length will mean a lot more mass.

Of course. I assumed that "15-23" would mean "average", so since the average band size is around a 36, that would probably mean "32D-40D" or something of the sort for "15-23".

Either way, the numbers seem absurd.

Volume of cone = pi * r^2 * h / 3.

Plugging in r1 of 3 and r2 of 2.5, and h1 of 36 and h2 of 34. Constants cancel out, that's an increase of 2.38 times in volume.

This is per cone ;)

I love Madonna too!

Exactly the way I'd expect nerds to discuss breasts :)

FWIW: Cup size is an increase in circumference, not length. And cup size is a relative measure. A "D" cup is supposed to mean that the fullest part of the breast is 4 inches more than the ribcage in circumference. So a 34D is going to be much less mass than a 44D (but, ironically, also a lot "fuller" looking relative to the rest of her figure). The last statistics I heard: The average American woman is about 5'4" tall and a size 16 dress size. More girth around the ribcage due to weight means "average" cup sizes that equal more mass because cup size is very much relative to that initial ribcage measurement. (I'm reminded that not long ago there was an article posted on HN apparently about women getting both shorter and fatter on average -- or so I gathered from the comments.)

That's the same point I tried to make.

It's a bit much for a D-cup but for a very obese woman, not that surprising. I had a girlfriend who was a 40(I think) DDD/E. She constantly complained about back pain from carrying all that weight on her chest.

Breasts the size of your head may look appealing, but to the owner, they're not a lot of fun!

The article punts on why women have breasts. For interesting speculation on that topic and several related ones, http://davidbrin.com/neoteny1.htm is an interesting read.

Desmond Morris, who wrote "The Naked Ape" and some other books, said some very interesting things about human anatomy and human sexuality.

http://en.wikipedia.org/wiki/Desmond_Morris

http://www.desmond-morris.com/

I think starting a bra comparison site with reviews and comments would be great.

There is actually a mass customization site called http://www.zyrra.com that lets women customize their bras and have them produced.

Wouldn't it be very subjective? Reviews of walking shoes are pretty useless, for example.

I don't know, but when I saw 5B annually my brain started to work very fast.

The timeless classic Why Women Have Breasts:

http://www.lloydianaspects.co.uk/evolve/breasts.html

What does it say about me that I first read that as "The Physics of Brass" and it was no less interesting?

I was going to post exactly that :).

For the first part of the article I was still waiting for a connection between breasts and brass.

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