SOAP NUMBERS AND VALUES
These key values help evaluate the composition and quality of finished soap. They are essential for formulation control, production consistency and quality assurance.
Soap Numbers and Values
The quality of a finished soap can be evaluated through several chemical and physical parameters. Among the most important values used in soap manufacturing and quality control are Total Fatty Matter (TFM), moisture, glycerin, Iodine Value and sodium chloride (NaCl). These values provide useful information about the composition of the finished soap and help manufacturers control formulations, production consistency and final product quality.
Total Fatty Matter (TFM)
Total Fatty Matter (TFM) is one of the most important indicators used to describe the composition and quality of soap. TFM represents the proportion of fatty matter present in the finished soap, mainly in the form of fatty acid salts and, depending on the product and analytical method, other fatty components. A higher TFM generally indicates a soap containing a greater proportion of fatty soap material and fewer non-soap components. TFM is particularly important when comparing different grades of toilet soap, laundry soap and filled soap. The standard TFM for Toilet soap bars is 78%, while for Laundry soap 72% is considered in Europe. Lower value of TFM are acceptable, considering the quality decreasing. As described in the previous chapter, filled soap has a very low TFM, up to 50%. These figures should be considered reference values rather than universal standards, as the required TFM depends on the formulation, product specification and applicable regulations.
Moisture Content
Moisture represents the amount of water contained in the finished soap and is normally expressed as a percentage of the total product weight. Water has an important influence on the physical properties of soap, affecting hardness, weight, drying, storage stability and processing behavior. The appropriate moisture level depends on the type of soap and the manufacturing technology. In industrial soap production, moisture control is particularly important during soap drying, cooling and finishing. Excessive moisture can result in a softer soap and increase drying requirements, while very low moisture can affect processing and the physical characteristics of the finished bar.
Glycerin Content
Glycerin, also known as glycerol, is naturally produced when triglycerides are converted into soap during saponification. The simplified reaction is:
Triglycerides + NaOH → Soap + Glycerin
The amount of glycerin remaining in the finished soap depends on the formulation and manufacturing process. In some industrial soap processes, glycerin is separated and recovered as a valuable by-product. In other formulations, part of the glycerin remains in the soap. Glycerin can also be deliberately added to certain products, particularly transparent and specialty soaps, because of its humectant properties and its influence on the characteristics of the finished product. An amount of 6 - 8% is presents in semi boiled soap, while full boiled soap usually has an amount up to 1%
Iodine Value
Iodine Value (IV) indicates the degree of unsaturation of the fatty acids present in the oils and fats used for soap manufacturing. A higher iodine value generally indicates a higher proportion of unsaturated fatty acids, while a lower value indicates a greater proportion of saturated fatty acids. This parameter is useful for evaluating the characteristics of the raw materials and their influence on the finished soap, including hardness, melting behavior and oxidation stability. The iodine value therefore provides useful information when selecting and controlling oils and fats for different soap formulations. For a standard hard soap, an Iodine Value of approximately 40–50 is generally considered a suitable range. Lower values indicate a higher proportion of saturated fatty acids and generally result in harder soap, while higher values indicate greater unsaturation and tend to produce softer soap. However, Iodine Value alone does not determine soap hardness, which also depends on the fatty acid profile, SAP value, Titre, moisture content and the overall formulation.
Sodium Chloride (NaCl)
Sodium chloride (NaCl), commonly known as salt, can be present in soap as a result of the raw materials and manufacturing process. The salt content can influence the physical properties of soap and the behavior of soap solutions. The amount of NaCl found in a finished soap varies according to the formulation, raw materials and manufacturing process. For this reason, there is no single value that applies to every type of soap. A value like 0.4% can be consider acceptable in toilet soap, while for laundry soap the percentage usually increase up to 0.8% or also little bit more. In quality control, sodium chloride can be measured as part of the overall chemical specification of the finished product.
Soap Numbers and Finished Product Quality
TFM, moisture, glycerin and NaCl describe different aspects of the finished soap:
Parameter ➞ Main informationTFM ➞ Fatty soap contentMoisture ➞ Water contentGlycerin ➞ Glycerol retained or addedIdonie Value ➞ Degree of fatty acid unsaturationNaCl ➞ Salt content
Together, these parameters provide a useful overview of the chemical composition and quality of a finished soap bar. They can be used by soap manufacturers to monitor production, compare different soap grades and verify that finished products meet their specifications.
Why Soap Numbers Matter
For industrial soap manufacturing, controlling these values is important for maintaining consistent product quality. Changes in TFM, moisture, glycerin or salt content can affect the hardness, appearance, processing behavior, stability and overall characteristics of the finished soap. These parameters therefore provide an important link between soap formulation, manufacturing conditions and finished product quality. Understanding soap numbers and values is essential for manufacturers, quality-control laboratories and professionals working with toilet soap, laundry soap and other types of solid soap.
Knowledge Content – Browse by Topic
01. WHAT IS SOAP
02. RAW MATERIALS USED IN SOAP MANUFACTURING
07. SOAP DRYING AND COOLING
08. SOAP FINISHING LINE
09. SOAP PACKAGING