When I go out for my walk, I wear a neck fleece. It has been my go-to face covering when exercising because it stays on my body and allows me to cover my mouth and nose easily when I can’t keep 6 feet away from people on the trail or sidewalk. Now, a new study out of Duke University says that it might not effectively block COVID-19 droplets.

Researchers report in Science Advances that my handy neck fleeces, as well as bandannas, allow more droplets to be expelled—speculating that the fabric may break up larger droplets into smaller ones as they pass through the material.

How did they figure this out? Researchers took 14 different types of homemade face coverings (including some masks) and had either one male speaker or four speakers wear each while standing in a dark enclosure. The speaker or group then would say the phrase “stay healthy, people” five times in the direction of a laser beam, which scattered light from the droplets released during speech. The droplets were recorded by cell phone camera and a computer algorithm counted them. (Supposedly the whole setup was about $200.)

Their preliminary findings show that N95 masks sans valves blocked droplet spread best (something we knew), but also that surgical, polypropylene, and handmade cotton masks were effective. (Luckily, there are easy ways to make your mask more effective.)

It’s scrappy science at its best, but one that needs to be expanded. “Our work was a demonstration of a simple measurement method, not a systematic mask study,” writes Martin Fischer, the study’s corresponding author, in a Q&A. “More work is required to investigate variations in masks, speakers, and how people wear them. We also want to extend our method to other droplet-generating actions, like coughing and sneezing.”

Looks like I will be either be trading my running neck fleece for a mask, or possibly, double up on them. I’ll let you know what I decide.