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Limitation of Fit for N95

N95 respirators will only approach maximum efficiency when tightly fitted to the face. Perfect fit is difficult to achieve and maintain in actual use. Face size and shape varies for individuals and facial hair also prevents a good seal. These factors together with comfort limitations previously discussed, often result in users failing to fit the respirator properly or distaining its use altogether. The table below demonstrates filtering efficiency of the N95 with variations in fit. Particles evading filtration were counted using laser detection instrument to measure particles in the size range of 0.1 to >1 micron. These sizes are inclusive of bacteria, virus, mold and fungus.

The N95 respirator is fitted over the mannequin face. Holes in the nose and mouth of the mannequin join to a sinus-like cavity inside the head. A tube through the rear of the mannequin head connects the particle counter to the sinus-like cavity. Particle counts were measured under conditions of a “Poor” fit, a typical or “Practical” fit, and a “Perfect Seal” fit.

The “Poor” fit is defined as the N95 not tightly fitted. This condition is evidenced by occasional small gaps between the N95 and skin as is commonly seen when the nose piece has not been tightly fitted, the N95 is not the proper size for the head and face shape, and/or the fit has been altered during wear. The gaps observed with the poor fit were measured to be less than 2 mm. The filtering efficiency of a poorly fit N95 was on average 46.8%.

The “Practical” fit was achieved by using an N95 well sized to the mannequin and optimally fitted as is specified in the package insert directions. To achieve a tight fit the nose piece was carefully adjusted. The 2 elastic bands stretched at a high tension with the top band around the head and the lower band under the ears and around the back of the neck. Under this condition no visible gaps more than 1 mm could be observed during actual wear. The average particle removal efficiency for this fit was 80.1%.

The “Perfect Seal” fit is one which cannot be practically achieved in actual wear because the seal around the face and nose would be prohibitively uncomfortable. For this experiment the N95 circumference was sealed with a bonding material over the manikin such that no air could go around the mask but only directly through the filter matrix. The Perfect Seal data shows the inherent ability of the matrix to filter out particles independent of N95 fit. The Perfect Seal fit gave 97.4% particle filtering which is in close agreement with the NIOSH specification of 95%.

N95 Filtration Efficiency as a Function of Variations in Fit

N95 Fit

Total Unfiltered Particles

(in 10 liters of air)

% Reduction from Ambient Air


No filtering, ambient air


Not applicable

Poor fit



Practical fit



Perfect Seal fit




The range of fits between Poor and Practical represent what are commonly seen in actual use. This data shows that fit is critical to N95 function and that under practical use conditions N95 respirators perform significantly below 95% efficiency