Actors and Actresses: Why do the actresses in Friends not wear a bra in many episodes?


Opinion 1:-

I'm answering this in general not in regards to "friends", from my perspective. 

Sometimes it's comfortable not to wear a bra!


Because it feels good, some sense of freedom, it feels very comfortable just to chill in your pajamas without wearing a bra.

Specially after a long tiring day at work, you should just come home, throw the bra away, get into your most comfortable clothes and sip a coffee and read your favorite book or watch your favorite serial. Trust me. This is heaven! 

That's why :)

Opinion 2:-

You may need to ask the producers. First you may not realize it but the appearance of brainlessness may be scripted and may not even be real. Its very common in TV and movies for both men and women to have false body parts but more often than not false breasts. In fact if you watch many TV shoes the breast on leading women get smaller as the episode moves forward or across multiple episodes because the early shots geared to getting as many eyeballs as possible as quickly as possible is driven by the women wearing more revealing, tighter tops or having falsies that go aware later into the series. 
A great example of this is in the new TV series Quantico. The main female has a fitted tailored and very tight version of what is supposed to be standard issue hensley t-shirts. Hers looks nothing like the other women in the background. The 2nd tier women have a more fitted shirt than the background women do as well. While the men generally have the same shirts. Look further and when the lead female is in other clothes they do not fit at all the same way as her padded FBI issued t-shirts do, because she is wearing props to make her breast seem larger and its fair to assume her nipple may be fake as well.
SO back to your question this ha more to do with keeping male viewers and keeping women viewers feeling like the show is edgy and somehow the female characters are stronger and more confident.
This is the same in fashion, modeling, commercial photography, advertising. There are many tricks used to enhance body parts as needed to accomplish goals and a lot o thought goes into bra or no bra, padded or not, nipple showing or not, enhanced air brushed muscles or not, fake tans or not its all part of the theatrical or advertising presentation.

Opinion 3:-

I think around that time, women started to protest that bras are not comfortable and women are not required to wear it if they do not want to. 

Also, bras are a sign of Conservative society trying to impose ideals on women, since there is nothing wrong with nipples and hence nothing wrong if their presence is felt to the observer underneath the clothes. Though, full display of nipples in public places is still illegal according to many laws, which could change soon as protests have started like 'free the nipples', of course in western socities like USA. Though full nudity is quite acceptable in many European societies like Germany.

The trend of not wearing bras continue still and is common now. Though eastern societies have not even started on it yet.

source :-