Hard soap

Hard soap refers to soap that is solid at room temperature and retains its shape well, unlike liquid or cream soaps. It's typically produced through the saponification process, where fats and oils react with a strong alkali, such as sodium hydroxide (lye), in a process called hot process soapmaking. The resulting mixture undergoes a chemical change, creating soap and glycerin. During this process, salts, which are important to the soap’s hardness, are created.

The hardness of soap is influenced by the types of fats and oils used in its production. For example, coconut oil and palm oil contribute to a harder soap, while olive oil produces a softer soap. The concentration of the alkali also plays a crucial role. The process is generally followed by rinsing to remove excess alkali and other impurities. After which the soap is cured, allowing excess water to evaporate and the saponification process to complete fully, resulting in a harder, longer-lasting bar.

Hard soaps are generally used for bathing, handwashing, laundry, and general cleaning purposes. They are appreciated for their durability, longevity, and ability to produce a rich lather when agitated with water.

Different types of hard soap exist, often distinguished by added ingredients such as fragrances, colorants, or emollients (skin softeners) to enhance their properties or appeal. Examples include milled soap (which undergoes an additional grinding and pressing process to create a very hard and smooth bar), castile soap (traditionally made with olive oil), and beauty bars (containing added moisturizers and fragrances).