I use a wide range of oils and butters in my cold and hot processed soaps. Though all of them are great for the skin and hair, they each have their own role to play in the soaps and shampoo bars that contain them.
Avocado Oil - A light, gentle oil that is full of vitamins (A, B1, B2, D, E, and lecithin) and essential fatty acids. It's absorbed very readily, leaves no greasy residue, and soothes, moisturizes, and heals dry, itchy, flaky skin, hair, and scalps. Due to its skin-soothing and regenerating properties, it's said to be beneficial to those who suffer from eczema, psoriasis, and sun-damaged skin.
Beef Tallow - Rendered beef fat. Tallow is rich in vitamin A and produces a creamy, hard, gentle, moisturizing bar of soap. It's a particularly effective addition to shaving soap, where it imparts an unparalleled creaminess to the shaving lather. Though I do like to use tallow in some of my soaps, most of my formulations are vegan friendly.
Castor Oil - A thick, viscous, very moisturizing oil that imparts an effusive creaminess and bubbliness to soap. It's a great addition any soap, but particularly to shampoo bars for its ability to create a satisfying, fluffy lather as well as its extreme conditioning attributes.
Coconut Oil - Solid below temperatures of 76 degrees, this oil is one of the few that offers significant cleansing properties due to its high lauric acid content. However, as a result, too much can be drying, since it has the potential to strip the skin of its natural oils. But, used judiciously, it is very skin-friendly. It also imparts hardness and a nice fluffy lather to each bar.
Kokum Butter - A highly prized hard, dense, emollient vegetable butter of Indian origin derived from the fruit of the Garcinia tree. Kokum butter possesses many characteristics similar to cocoa butter (high vitamin E content, promotes skin regeneration and elasticity, imparts a luxuriant creaminess to soap lather), but is non-comedogenic (does not clog pores). It's wonderful stuff.
Olive Oil - An oil with a long soaping history, olive oil provides great conditioning for the skin and is extremely mild. Soap made with 50% olive oil or more is known as castile soap, named after the region of Spain in which it was allegedly invented.
Palm Oil - Palm oil is a great soap base in combination with other oils that lends hardness and a stable, creamy lather to soaps.
Safflower Oil - A very light, silky, highly moisturizing, and gentle oil that promotes a stable lather.
Shea Butter - One of the most renowned soaping and cosmetic butters in existence (for good reason), shea butter is an off-white, fairly soft, vegetable butter derived from the fruit of karite tree. It's full of vitamins A, E, and F, all of which promote skin and hair regeneration. My shea butter is unrefined to ensure that all of its properties are intact. It's a highly moisturizing butter that has historically been used to treat/mitigate a wide host of ailments such as eczema, psoriasis, sun burn, scars, stretch marks, wrinkles, insect bites, and even small wounds. In addition to its healing properties, shea butter provides deep conditioning for the skin and hair. This conditioning improves skin softness and elasticity, reduces dandruff, and adds luster, strength, and softness to hair.
Stearic Acid - This is an acid that is found in other oils and butters, most prominently in shea, mango, kokum, and cocoa butters, and beef tallow (however, my stearic acid is ENTIRELY OF VEGETABLE ORIGIN) that adds creaminess and hardness to soap. I use this in my shaving soaps and some shampoo bars to enhance the texture of the lather.
Vegetable Glycerin - A viscous, clear, emollient humectant derived from vegetable lipids. Glycerin is a byproduct of soap-making and is naturally present in soap (however, big soap companies deliberately remove the glycerin from their soap to sell separately). It's highly moisturizing and does not saponify (turn into soap). I typically use a small amount of glycerin as a medium in which to mix my pigments, but don't add too much in addition to what occurs naturally to my bath soaps, as too much additional glycerin would compromise the feel and texture of the soap. Where extra glycerin really shines, though, is in shaving soap, where its humectant properties help keep your beard nice and hydrated throughout the shave. In addition, glycerin makes shaving lather stronger and less subject to breakdown.