Transparent soap is clear soap with a high glycerin content. Often referred to as “glycerin soap,” transparent soap is less drying than opaque soap, and can have additional emollient oils added to it, such as shea butter or jojoba oil. The first mass produced clear soap was Pears® brand, introduced in 1807 and still available as of 2010.
Glycerin is a humectant, which means that it attracts moisture. This property of glycerin soap is what makes it more moisturizing than opaque soaps that contain less glycerin. Referring to transparent soap as glycerin soap is slightly misleading because all soap contains glycerin, a sugar-based compound found in all animal and vegetable fats. Whether it's clear or opaque, homemade and handmade soap usually has all the glycerin in it. In commercial soap-making, the glycerin is extracted and used in more expensive soaps and creams.
Transparent soap is so gentle that it is often recommended for people with very sensitive skin, such as babies, small children, and people with allergies or dermatitis. Soap with a high glycerin content rinses more easily from the skin and doesn't leave a film that could cause irritation. Additionally, glycerin soap is generally less expensive than other moisturizing or anti-aging beauty bars.
Soap is made from lye mixed with an animal or vegetable fat, such as tallow or olive oil. This is called cold-process soap-making, where the fatty acids in the soap react with the alkali in the lye. The oils become hard in a process called saponification. To extract glycerin, hardened soap is shaved and melted again. Salt is added, which causes the soap to curdle and separate from the glycerin. Glycerin can be added to soap to make the bar clearer and more moisturizing. To do this, the soap-maker melts soap shavings, then adds high-proof alcohol, sugar, and glycerin. The soap is allowed to harden, and then is melted several more times to remove any extra water that causes the bar to look cloudy.
It can be challenging to learn how to make soap with the cold-process method, so many craft stores sell blocks of “melt-and-pour” soap. These blocks contain varying amounts of glycerin, and some are already transparent. Melt-and-pour products are cold-process soaps that can be re-melted to add additional ingredients, such as essential oil, coloring, or other decorations before pouring them into attractive molds. Glycerin can also be added to melt-and-pour soap to make it even more transparent.