An additively manufactured heat exchanger configured to transfer heat between a first fluid and a second fluid includes a first channel with a first wall configured to port flow of a first fluid and a second channel with a second wall configured to port flow of a second fluid. The heat exchanger also includes a barrier channel containing unprocessed build powder provided by the additive manufacturing process and is located between the first wall and the second wall. The barrier channel is configured to prevent mixing of the first fluid and the second fluid when one of the first wall and the second wall ruptures.