Solid shampoo bars are quite popular for traveling and are a mainstay at Lush products. You can make your own for a fraction of the cost of a lush bar and without all the icky parabens and SLS. I found a website that not only provides the ingredients but also a nice tutorial. It's very similar to making cold process soap, but the base oils are a little different - more castor, jojoba, avocado and wheat germ oils for their conditioning properties. Panthenol is another good addition. The recipe and insructions from soap kitchen don't have all those oils but it sounds like a good starter recipe.
INGREDIENTS12 oz (340g) of cold, clean water
125g of sodium hydroxide (caustic soda) beads or pearls
8oz (227g) olive oil (preferably pomace grade but virgin or extra virgin will do)
8oz (227g) coconut oil (hard variety)
6oz (170g) palm oil (hard variety)
6oz (170g) castor oil (B.P. grade)
3oz (85g) sweet almond oil
1oz (28g) jojoba oil
Emmy Gabriel notes: "One drawback to shampoo bars is that they will leave residue on your hair after several uses. This problem is easily remedied by using a Rinse after every few washes. A simple rinse can be made as simply as combining 1 part Apple Cider Vinegar with one part Water. However, you can create more elaborate Rinses by incorporating teas, Infusions, Hydrsosols, Extracts, or other specialty ingredients. If you aren't crazy about the aroma of Apple Cider Vinegar, try adding a few drops of Lavender Essential Oil to your rinse. Also, check out our Herbal Hair Rinse Recipe or Ayurvedic Hair Rinse Recipe for something extra special."