If you have a properly fitted mask like and wear it correctly, it truthfully won't do much more. According to what I saw, the reasoning for the recommendation is due to the fact that most people aren't doing that. Apparently their research into a solution was that a double mask is the most bang for the buck. Adding a second over the first increase the contact to skin of the first and greatly helps to seal off gaps. Much less particles going out and less particles coming in between the better seal and extra layers of fabric.