The idea started in Italy, the European country worst-hit by the coronavirus pandemic, with hospitals in other nations taking note and adding their own specific medical parts to make it work.
One such is the Erasme Hospital on the outskirts of Belgium's capital Brussels. It is attached to the city's ULB university - and through it to a private spin-off, Endo Tools Therapeutics, whose knowhow in 3D printing for medical use has proved invaluable.
"They are to be used for patients with severe respiratory problems. The aim is to avoid having to intubate the trachea of the patient and put them on a respirator," said Frederic Bonnier, a respiratory physiotherapist at the hospital who also teaches at the university.
He spearheaded the design of a custom-made valve that fits to the top of full-face masks, where the snorkel is meant to go, allowing them to connect to standard BiPAP machines that feed pressurised air into masks.
This helps prevent the collapse of alveoli, lung air sacs needed for the intake of oxygen into our bodies and the exhalation of carbon dioxide. Pneumonia brought on by COVID-19 inflames the lung membrane and fills those sacs with liquid.