Would big bra cup size women wear plunge push up bras with padding?

First, “boobs” is slang and offensive to many women. If you want to design bras for women customers, the proper word is “breast” and sewing patterns for clothing like blouses and dresses speak in terms of the “bust” and “chest" measurements. I am going to assume that you do not mean to offend and that perhaps English is not your first language, but please be aware particularly if you are male that many women are uncomfortable speaking about undergarments to men or any strangers and saying “boobs” and other slang words for body parts can mark you as unprofessional and cost you business. You can search online for “how to measure for sewing” and find forms to fill in using the proper terms in English for men and women for different types of clothing.

Padding in the bra cup is not a primary consideration to whether the design of the cups is properly shaped and supportive enough to hold the breasts in a good position in combination with the straps. A bad cup and strap design will become more obvious when tested in the larger sizes if one is designing bras and padding cannot fix a bad design. There are far fewer “plunge” designs in larger cup sizes in part because they are much harder to design. Some firmer padding can be used to help stabilize a bra cup, but the shape and strap placement must be correct also.

It is more like an engineering problem to sew a larger size bra than designing a simple dress or shirt because other garments merely cover the body in most cases and a bra must support and secure the breast into a certain position. In fact, there is a growing movement amongst women who sew at home to study bra making because commercially mass produced bras are such a problem when it comes to finding a proper fit and after that hoping for styles that one likes. Women get angry that pretty bras that fit properly on larger sizes often cost $50-130 US.

Another factor to consider in larger sizes is that women with larger sized breasts that are natural have a lot more variation in shape and a whole lot more movement that must be taken into account versus artificially enlarged breasts which are bags of saline that sit more or less in one position on the chest and don't require as much support from a bra. A one piece molded cup bra with a little padding is made currently in larger cup sizes, but the true plunge styles I have seen require 2 or 3 piece cups for a more supportive fit because the stability is lowered as the section between the breasts gets lowered. It is like a bridge design that cannot use more than one horizontal support on one side yet must bear the same load as a bridge with supports on two sides.

In addition, while a customer with a smaller breast may like adding the illusion of additional size with a padded cup, often a customer who is already large in the bust will not want to look larger at all. They want bras engineered for good support but not enhanced size. Extra padding will not restrain a large breast in a poorly designed cup and it could cause a customer to skip that design if the padding adds too much bulk.