I have been making soap since 2002 by the melt and pour and I have never heard of an INS Number. Maybe many of the more experienced soap makers have. But if you are like me and have not, I recently found out more about this through an entry on The Soap Queen's site called INS Numbers for Soapmaker's. According to Anne-Marie, an INS number refers to a numerical value that explains or describes the properties an oil will have when reacted with sodium hydroxide to make bar soap. It relates to the degree of unsaturation and the molecular weight of the oil. Full disclosure: I don’t use INS numbers. I don’t find that they relate well to a finished batch of soap and how it will be perceived by me (or anyone) in the shower.
In reading this article, I have learned that it more for the soap maker who makes their soap by the cold process method and that is maybe why I have never heard of it. But it is an interesting and informative article to learn about what INS Numbers are and what the benefits of using them. If you are primarily a melt and pour soap maker the information may be confusing to you, so you may want to pass on this information. But for those who make their soap by the cold process method, I would recommend you read the article.