I have had a few people recently ask me the difference between melt & pour and cold process soaps. Many are under the assumption that Melt and Pour (MP) are inferior to Cold Processed (CP) soaps. Let's address this by first defining the two and then discussing the benefits each yields for the soaper and for the consumer.
Melt and Pour (sometimes referred to as Glycerin soap).
Melt and Pour is a soap making method that involves taking a pre-made soap base that can be melted in either the microwave or a special melt pot. Then additives are carefully selected and measured and added to the base to create the desired effect. Additives include essential oils, fragrance oils, colorants, and/or botanicals to name a few. MP bases do vary in quality. You have the type you can purchase at craft stores that are fine for weekend crafts with the kids and even for testing. However, the serious soaper will use bases that can be bought in bulk and are of superior quality, formulated for specific needs. They can be simple or challenging to create. They can be decorative and ornate or just plain fun.
At Soap Scent-sations I use a quality bases that are SLS free (that's another topic all together). Each color and scent is tediously selected and can be as simple as my Soap on a Rope or layered and molded into fancy layered soaps such as the Fleur de Lis collection. I love how simply clean my skin feels after using a MP bar. My kids especially like the animal and bug shaped soaps. That helps make bath time fun for them and I know that by using quality bases, I am not compromizing their delicate skin with unnecessary chemicals.
Cold Process Soap (many know this as Lye Soap).
Cold Processed soap is a method of soap making that involves using sodium hydroxide (or lye) in combination with oils (fats) to create a cleaning agent we all know and adore--soap. The beauty of CP is that you get to be involved with it from the very beginning. You select your oils and butters and measure them out in the proportions that give you the properties you desire. I won't bore you with the chemical reactions and properties that allow all this to happen, but know that the right combination is important to the CP soap maker. Too much lye can make a harsh bar that is either completely unusable or drying to the skin. Excesses in oils can clog pores, etc. And don't think that cold processed bars are frumpy and without their own amount of creativity. The practiced soaper can create beautiful swirls of color, fanciful layers, and highly aromatic bars of soap using the cold process method.
Me, I like a nice hard, long lasting bar so I use plenty of coconut oil. But I also like to feel soft when I am done so I balance the coconut oil with skin happy oils and butters like olive, jojoba, and shea. To me, each batch is it's own beast! And I like them all for different reasons. The Shea Butter Soaps are one of my favorite recipes. They are the perfect balance for my skin. But the Gardener's Soap is very popular for its extra scrubbing power.
Both MP and CP soaps contain glycerin. Glycerin is a naturally occurring by-product of the soap making process. Glycerin is a humecent (draws moisture to the skin). That is one of the reasons handmade soaps do not dry skin out like commercial beauty bars. They start as soap, but the natural glycerin is leached out and sold as a separate product. Don't be wary of soap that lists sodium hydroxide or lye in ingredient lists, it's part of the process and completely necessary to soap making. While both use lye in the creation of soap, neither MP nor CP soaps contain lye in the end. The chemical process involves the lye fully incorporating with the oils.
As you can see, both MP and CP methods of soap making can be challenging to the creator and beneficial to the consumer. I don't think one is especially better than the other. We all have our preferences. In the end, it's all just soap! But do look at ingredient lists. Be on the look out for chemical lathering agents in MP and certainly request ingredient lists on CP soaps. Both can work for you if you know what you are looking for.