On the Bra Making Forum the adjustment advice to “split the bottom cup” is given a lot. Splitting the lower cup address issues of pointiness and to help create extra volume. However, if you’ve never done that alteration before you might not know what that means. This simple tutorial will guide you through the basics. It’s a quick and simple pattern manipulation which gives you more options when it comes to altering your bra pattern to fit.
This tutorial assumes you will be starting from a basic 2 piece bra cup but this method can be used with other styles also. The example cup is from my basic 36B 2 piece bra block. The cross cup seam hits ~10mm above the point of bust. The cup piece is shown without seam allowances.
The first step is to find the POB where you will split the cup from. Usually, this is marked with a notch. If it does not find the uppermost point of the cup and mark there. You then want to divide your cup in half based on this point. 95% of the time you will mark straight down at a 90-degree angle to the POB. However, this is not necessarily a rule.
The next step is to split the two pieces apart and decide where and how much fullness to add. This will depend entirely on your pattern and what you are hoping to achieve. I prefer to place my fullness 2/3rds of the way up from the bottom of the cup. Other methods have you add at the halfway point but from my experience that ends up being too low and the breast will start to sink down in the cup. I am adding 6mm on each side measured at a 90-degree angle from where the cup has been split. This is what I would recommend you start with if you are not sure how much to add.
Draw line using a french curve. Make sure to measure both sides to ensure they are the same length. I recommend adding a notch at the fullest part of the cup. You might want to notate how much fullness was added so you can keep a record of your pattern changes.
That’s it! You are done. All you need to do now is add seam allowance and you’re ready to whip up your new bra.