Oils Do Not Seal Water In Hair Or Prevent Water From Being Absorbed By It

I keep seeing the opposite which is a misconception, repeated on the Internet, in spite of evidence to the contrary.

Here is a research study reference I have used before, the full pdf, the cached copy and the abstract.

From Page 142 of the pdf, colour added by me,
"Figure 6. Water vapor sorption isotherms for hair samples with varying thicknesses of surface oil films. Samples with thicker films absorb less water vapor compared to thinner films. Mineral oil-treated hair consistently absorbs less water vapor compared to coconut oil-treated hair, in both cases." 
What this means is that you do not need a lot of mineral oil on your hair to prevent frizz or keep needed water in your hair, which can evaporate quickly otherwise and it is supported by my results and the reported results of many others. 

From Page 145, colour added by me,
"Our results using the DVS method indicate that moisture sorption behavior is not influenced by the oil that has penetrated into the cortex." 

There is more information here in the COSSMA reference about oils used on skin.

Anyone who uses oil, or silicone on damp, or wet hair knows this as fact too.

If oil, or silicone did seal water in or out of hair,

1. Hair would not dry and it could not become wet after oil, or silicone was applied to it.

2. Hair would not become "poufy" or frizz in high and low humidity.

Natural oils and silicone have different properties. Mineral oil can work much better than vegetable oils, natural sebum, or silicone to prevent frizz and moisturize hair longer because of its properties. It is also a natural oil.

It is not just about the word seal. I have seen the word prevent used incorrectly as well.

Less water absorbed and water retained in hair is accurate and I have also seen that said online, far less often and worded differently.

With catnip and mineral oil baby oil use, my hair dries fairly quickly. It is about waist length long again and although relatively thin, it air dries completely in about or less than one hour and a half, after briefly being towel blotted, post-washing.

See Also
This blog post and this one