OK so here's the deal. There are 2 styles of handmade shampoo that you can make or purchase. One is a modified cold process soap (where lye added to oil and causes the saponification into soap and glycerin. The heated and melted soap "batter" is poured into a mold and then sliced into bars.). Typically you use a combination of very lightweight oils so that it doesn't weigh down your hair but remains very moisturizing. Additives such as shea and cocoa butter are avoided as they are too heavy and greasy for the hair. We already know that cold process soaps are fabulous for the skin so why wouldn't it make sense that it would be good for your hair as well. Now I have made these kind of shampoo bars and I can tell you they do work well. They are not irritating to the scalp and don't dry out your hair. They even work with color treated hair. The single biggest downside is that their pH is quite high. You cannot make a cold process soap without of pH of 8-9. Even adding citric acid to bring the pH down doesn't help. Although this pH is great for skin, hair wants a pH closer to 6.0.
This is where surfactant based shampoos come in. Surfactants are very gentle but effective cleansing agents that can be added with a variety of other additives such as humectants, emollients, conditioners, detanglers, clays etc. The wide variety of additives available make it possible to customize your shampoo bars easily for different hair types. There is no lye used in this type of shampoo. They are heated gently to combine all ingredients and then pressed into a bar. The pH in these bars depending on the surfactant used may be 6.0 automatically upon completion, but if not can easily be adjusted with the help of citric acid.
This latter shampoo is the shampoo I sell currently. I used to sell the cold process type, but my research and my personal experience now has made it clear to me that the surfactant type shampoo is a healthier choice for your hair and feels much more soothing on the scalp. The lather is amazing.
If you haven't tried a solid shampoo you should. You don't know what you're missing. It is amazing on your hair, one bar lasts for at least 30 washes and it's absolutely THE BEST CHOICE FOR TRAVEL. Why pay for all that water in a liquid shampoo and why buy yet another plastic bottle. Begin your nearly zero waste journey.