Environmental control systems, airflow interleavers, and methods. The environmental control systems include an airflow interleaver and mix manifold comprising a mixing chamber. The airflow interleaver comprises a first airflow guide structure configured to guide a second airflow towards a central axis of the mixing chamber and a second airflow guide structure configured to guide a first airflow away from the central axis. The methods include channeling first and second airflows to the mix manifold, mixing the first and second airflows, which includes guiding the first airflow away from the central axis and guiding the second airflow towards the central axis. The airflow interleavers include a tubular body, and a plurality of converging airflow guides and a plurality of diverging airflow guides extending from the tubular body and collectively being configured to interleave first airflow streams flowing from the tubular body with second airflow streams flowing external to the tubular body.