Adding extra oil to cold or hot process soap after it has traced or cooked is called superfatting. Superfattng typically is used to make soap more moisturizing. I usually superfat soap that has a good deal of coconut oil, say 20-30%. However, soap may be superfatted regardless of whether or not there is coconut oil in the formulation. Of all the oils used in soapmaking coconut oil is one that is a mainstay of many formulations owing to the fact that it creates a super hard soap and produces a soap that lathers well. The downside to using coconut oil is that it has a high percentage of lauric acid, a medium chain triglyceride, which renders it a great cleaner but drying to the skin. Therefore formulations that have coconut oil - in any amounts but especially in amounts over 20% should be superfatted so that it will not be drying. The addition of the extra oil that does not take part in the saponification process but rather at the end of trace or the cook is small, usually anywhere from 1-5% of the total oils used.
One other big reason to superfat natural soap especially cold process soap has to do with the soap's pH and its drying effects on the skin. Regular cold process soap, though a natural product has a high pH (9.5). Skin on the other hand has a low pH (4.5-6) in the acidic range. The difference between the low pH of skin and high pH of natural cold process and this incompatibility is what causes soap to be drying to the skin. In order to make soap more compatible with our skin's pH we should superfat natural cold proces soap by adding fatty acids (oils).
Since normal skin is usually around 4-6 on the pH scale, having soap that is considerably above that level can be a big deal especially when we consider that certain skin conditions flourish at higher pH�s (alkaline) than at acidic levels <7.5 . One example of these conditions is P.acnes which is a gram positive bacteria found on all skin but proliferates in larger numbers on skin that is more alkaline. Conversely, if the pH of the skin is lowered through topical application or soap products that are closer to the natural acidic pH of skin then, these numbers fall.
Another way to correct the pH of soap to be more compatible with the skin's pH is to cook the soap. The hot process method produces soap that has a lower pH and thus is milder to use than soap that is cold processed. In addition, any method that uses half cook/ full cook method will be gentler to the skin than full cold process soap.
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