paper thin
1. (hyphenated if used prenominally) Literally, having a thickness comparable to paper; exceptionally thin. This blade is so sharp that it can cut through a tin can with a paper-thin incision. Young lady, you are not going on a date wearing a dress as paper thin as that!
2. By extension, quite meager, inadequate, or feeble. John is always offering some paper-thin excuse as to why he's late. The promises the new president made in her campaign were exceptional, but so far her results have been paper thin.