We are always asked for padding in our bras - for discretion, lift, extra bulk, but it's a tricky one to navigate where you are only using 100% natural materials.
We've trialled cotton and wool wadding, but in both cases, the material continues to shrink multiple times, and there's only so many times we can ask our suppliers to pre-wash before they stop returning emails. We are looking at making some removable inserts, as slight shrinkage in these matters less than if it's sewn into the body of the bra, and not everyone wants the extra layer. We are currently trialling these with cotton fleece, as well as a new hemp and tencel wadding lined with cornstarch. It's an ongoing thing!
I wanted to share below how padding in conventional bras is made. Yes, they make perfectly round cups, but what you're seeing here is a great big piece of plastic being melted to mould into a cup shape. It works, but it's 100% plastic, and you're going to wear it against your body. There's so much around these days about the levels of BPA in synthetic bras I don't know why you'd want to risk this every day.