KCKT works well as a leave-in for me but I have to be careful not to overdo it (less than a dime-size is enough; I use a teeny-tiny dollop). Anything else, and my hair goes limp. It's very thin and fine and easily weighed down.
If you want to use a leave-in but find traditional ones too heavy, I had good luck with Jane Carter's Revitalizing Leave-In. It's a lightweight spray, and I've been thinking of stealing it back from DD.
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