My favorite is coconut oil and olive oil simply because I always have those two oils in the house for cooking. They're also the two oils that are supposed to actually penetrate the hair strand, so I feel like those make the most sense for a treatment and not just sealing. I use these oils with the ROO method and sometimes I mix them together and heat them up and do a heavy pree poo treatment. I have grapeseed and it's good as a sealing leave in, but I mostly use that one on my face.
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