I love these solid bubble bars!  These are made without glycerine so they harden up nicely and you don’t have to wrap them up tightly. 

Solid Bubble Bath Bars

200 g arrowroot powder (or corn starch)
200 g baking soda
100 g SLSa
200 g liquid surfactant (I used Super Mild Surfactant Blend™ from Ingredients To Die For)

colorant and 2% fragrance

Mix all of the ingredients together until a dough forms.  Mold or form however you want.  Depending on how thick/big they are they might take a week or so to totally harden.  Even then the inside might still be a bit moist when you break them up.   

Have fun!