A new method for using e-cigarettes called “dripping” is becoming popular among teens. A report published in Pediatrics finds one-quarter of U.S. teens who use e-cigarettes have experimented with dripping.

This method creates denser clouds of vapor, HealthDay reports. The health effects of dripping are unknown, according to the report’s authors from Yale University School of Medicine.

Regular e-cigarettes produces inhalable vapor by slowly drawing liquid into a heating coil through an automatic wick. Dripping involves placing drops of e-liquid directly onto the heating coil, and inhaling the cloud of vapor that is produced.

Among teens who tried dripping, 64 percent said they liked the thicker clouds of vapor it produced. Almost 40 percent said they thought it produced a better flavor, while 22 percent were simply curious to try it.