How-To for Covid-19

Mask Ratings

Following are the ratings for different types of masks. The ratings are from work by Phillip Clapp, a research assistant professor at the University of North Carolina at Chapel Hill, and his colleagues.

Reference data for N95 masks, Surgical masks, and Shoptowel Masks.

Reference for KN95 masks

N95 2 Tie Straps 95%
Jia Hu Kang KN95 Ear Loops 85%
Blue Shop Towels 2-Layer tight fit 75%
Surgical Mask 2 Tie Straps 70%
Guangdong Fei Fan KN95 Ear Loops 53%
Blue Shop Towels 1-Layer tight fit 50%
Surgical Mask Ear Loops 40%
Cloth Mask Weave or Material
too variable
to test
0% to 40%
estimate from
other sources

More references:

January 2021 EPA Tools and Resources Webinar: Effectiveness of Medical and Cloth Masks for COVID-19 Protection

CDC Data Tracker in Casses per 100k Poulation

The CDC link above is best viewed on a computer. The map of the United States showing cases per 100k population does not allow display of detailed state data on a cell phone. Clicking on the state using a mouse on a computer does display the detailed data.

Maps shown in media outlets often show number of cases in percentages, which is invalid since it ignores the size of the population of the state.
A group of 100,000 with 2,000 cases is a 2%.
A group of 1,000,000 with 2,000 cases is a 0.2% .

Construction of Two-Layer Shop-Towel Mask

Towel material is from Scott Shop Towels Original, number 10-29-625-0-02, Distributed by Kimberly-Clark Global Sales,LLC Roswell, GA 30076-2199.

Rubber bands are size #64, 3-1/2 x 1/4 from Alliance Rubber Company,P. O. Box 20950, Hot Springs, AK 71903, sold on

Modification of Adult KN95 Mask To Fit Child

Copyright Dale Thompson,
December 31, 2021 through
last revision on January 1, 2022.