Babies breath (also known as gypsophila) is a standard favorite for use as a filler flower in all kinds of flower designs. It is relatively cheap and looks sweet tucked here and there in bouquets.
Years ago babies breath was used all over a bridal bouquet design. To prevent a dated look, use florist tape to gather the stems together and create a tight, clustered stem about the size of a small rose head.
Scatter these gypsophila stems across your bouquet, tucking them under the rose heads in a random manner.
Gently insert these stems, taking care not to touch the other flower heads any more than necessary.
It is a great concealer flower to cover up the edges of the bouquet holder.
Be sure to inspect your bouquet from the sides as well as the top, filling in the holes where needed.
The overall design is taking a lovely mounded shape (rather than flat), mimicking a natural hand tied look.
Don't go over power your bouquet with too much babies breath - just enough to fill in the gaps in the overall bridal bouquet design.