Read an article the other day about the differences in oils that are good for moisturizing the hair versus sealing the hair. Here’s the basic info. The article is from http://www.naturallycurly.com and is titled “Is that oil a moisturizer or a sealer? You should know the difference” by Sabrina Perkins, if you’d like to read the whole article.
Oils that penetrate deeper into the hair shaft to moisturize: coconut oil, sunflower oil, and palm kernel oil
Oils that may also penetrate slightly beyond the outer cuticle, but are better used as oils that seal, coat, and lubricate the hair to prevent moisture loss and increase softness: olive oil, avocado oil, and argan oil
Oils that contain very bulky lipid chains which make the molecules bigger, and highly unlikely to penetrate, but are great to enhance shine and lubrication for ease of combing: jojoba oil and rice bran oil
A 2005 study confirmed that heat can help oils that are already likely to penetrate the hair to penetrate faster.
The level of penetration is determined by the size of the oil molecule and polarity. Coconut oil, being the most penetrable of natural oils, is very high in triglycerides containing short chain, fatty acids, making the molecules small enough to penetrate the cuticle layer. It is also more polar (positively charged) than most oils, which makes it more attracted to the negatively charged proteins in hair.