I just did a quick test with Reflector and it looks like string interpolation is turned into String.Format(..) calls, which in turn will use StringBuilder. This

I just did a quick test with Reflector and it looks like string interpolation is turned into String.Format(..) calls, which in turn will use StringBuilder. This makes sense as String.Format(..) understands all the string formatting placeholders. > BTW there is a typo: "passed in my the calling code" should probably be "passed in by the calling code". Thanks for spotting that, I'll fix it in a bit