So my hair is somewhat thin.Curly coilyish. If I got box braids with extensions would it do damage ?
Long as the braids aren't too tight then it won't do any harm.
. Do you think size matters ?
It depends why your hair is thin. If it's from illness and medication don't do it. If your hair is naturally thin i.e. it's a genetic trait then don't do them tight. Braiders often insist that the only way to keep braids neat for a long time is to do them tight. Your braids shouldn't be in more than 4 weeks and 6 weeks at a push unless you want your hair to fuse and tangle.
I believe it's less about size and more about weight. If your hair is naturally fine and you don't have much density, you have less strands on your head than average. Installing box braids using traditionally heavy added hair could pull on the strands you have and actually cause damage. Opt for a lighter hair type like Afro Kinky (formerly known as Marley hair), that won't weigh down your fine tresses.