Are open-ear or in-ear headphones better for running outdoors?

For road running, most safety-minded reviewers favor open-ear or bone-conduction designs because they let you hear traffic, cyclists, and other runners. In-ear buds with strong passive isolation or ANC seal you off from your surroundings, which is fine on a treadmill but riskier on the street. The tradeoff is sound quality: open-ear designs almost always have weaker bass and lower max volume in noisy environments.