This isn't quite correct. An N95 must filter 95% of all tested particle sizes (individually) to be certified. In general these types of filters do best with r

This isn't quite correct. An N95 must filter 95% of all tested particle sizes (individually) to be certified. In general these types of filters do best with really small particles and really large particles. There is a size in the middle that in practice is between 0.1um and 0.3um that is called the Most Penetrating Particle Size, i.e. the worst case size, and the N95 must filter 95% of that size. For smaller and larger particles, an N95 will filter better than 95%. For Covid, my understanding is that the infectious particles you're worried about are generally larger than the MPPS and that generally an N95 will filter 99%+ of these. As was shown in the article, ultimately it becomes all about fit, because even if only 1% of the air is getting around the mask, improving the filter doesn't help that much in overall efficiency. If you want better than this, you need to go to a higher rated mask with a better face seal like an elastomeric mask with a rubber seal.