Start by melting the chopped base as usual (45 seconds in the microwave) and mix in about half a dropper or 2-2.5 milliliters of fragrance and about 1/4 tsp of shredded loofah per melted mug of soap. I used a green loofah-- we no longer carry colored loofah at Bramble Berry, but if you stop by Otion you can pick up violet or green while it's still here. The amount of loofah is really up to you--go with the "less is more" mentality, or throw a bunch in there for extra exfoliating action. I went with a pretty happy medium so that there's enough space between the loofah particles to make them stand out from one another.
The key to getting your loofah to suspend in the soap instead of sink to the bottom is to keep mixing until the soap is fairly cool and slightly thick but not clumpy. You know, it's the phase right before you end up frustrated because you have to re-melt it (usually followed by a "Grr!" or some form of bad word). Pour into the mold, spray with rubbing alcohol and pop it in the freezer for a few minutes to let it set up quickly.