Melt the soap base in the microwave in 10 second intervals.
Add the glycerin to the melted soap base and mix with a hand mixer until it becomes frothy. If it gets too hard, pop it back into the microwave.
Add your foaming bath butter in with the glycerin and soap mixture. Mix this with your hand mixer until it is a light and fluffy consistency.
Add fragrance oil and mix again with the hand mixer to fully incorporate it.
If you are adding color, you can do this now. If you would like to add multiple colors, separate the base into different containers and color as desired.
Add the sugar and mix well. You are going to want to scrape the edges of your container with a spatula to ensure everything mixes in.
Place your whipped sugar scrub into a piping bag. You can scoop this into the jars, but I find that the piping bag is a cleaner process and the finished product looks nicer.
Pipe the mixture into your containers and enjoy!