This is a beautiful illustration what bra extenders do to former good-fitting bras.
If one gains weight, generally causing the need for bra extenders, the breasts generally get heavier, as well. Pair the extra weight w/ an ill-fitting bra, the back begins to ride up & straps slide off...changes the integrity of the original bra size....and being more uncomfortable in the long run.
If one is in an interim period of weight loss/weight gain, I would suggest wearing a popular pull-on bra (Ahh/Genie) until weight is stabilized, then invest in a proper fitting bra w/ supportive cups.
Being a 'better-bad', a pull-on bra supports the breasts much better than an extender could ever achieve.
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DO BRA EXTENDERS WORK?
January 23, 2014 by Tomima

We women go through so many physical changes in a lifetime that it’s no wonder our bra size can fluctuate. Sometimes the cup fits just right, but the band on your bra suddenly feels too snug. In this case, many women turn to bra extenders. Bra extenders are just rectangular pieces of fabric that typically hook onto the hook & eye closure of the bra back to extend the length of the band 1-3 inches. During pregnancy, certain times of the month or if you experience a sudden weight gain, you might think a bra extender is the solution.
And yes, these extenders can be a good solution, but should only be a temporary one. Any advantage you gain in band size will be countered by problems with the straps. More than half of the women surveyed in HerRoom’s Know Your Breasts bra finder say they have problems with bra straps slipping off their shoulders. Now what, you’re asking, do bra extenders have to do with bra straps? A bra extender changes the design of the bra, specifically strap placement. Adding a few inches to the back of the bra moves the straps out in the back so they sit closer to the ends of your shoulders. This could lead to a chronic problem with straps slipping.
A good example of the way extenders change the bra design is the leotard back bra. Leotard backs are specifically designed to create the right amount of tension to keep straps at a particular angle. When you add a bra extender, you’re changing that tension and ruining the suspension built into the bra. I liken using bra extenders to walking around with a dress not zipped up all the way: yes, it fits, but it throws off the shoulders and the lines of the dress.
So, the moral of this post is that you should really find your correct band size instead of putting a band-aid (or bra extender) on the problem. Sure, they’ll do the trick for a quick temporary fix, but you’re going to run into other fit issues, like the slipping straps I mentioned above. A quick reminder–when you go up a band size, you need to go down a cup size to maintain the same cup volume. Equally, when you go down a band size, you’ll want to go up a cup size.