If that sounds all kinds of claustrophobic, apparently it “DOES NOT COVER THE MOUTH… Instead, it surrounds the mouth, bringing the lips together with a light, elastic tension that helps to maintain lip closure and ensure nasal breathing.”
Article source: https://www.huffingtonpost.co.uk/entry/gwyneth-paltrow-nose-breathing-strips_uk_636d20eae4b021a40391fb9f