About the ULTRA FIT™ Mask

The Problem with Conventional Masks

Katharos Labs was founded during the COVID-19 pandemic to create more effective personal protection for community use (see the story here). It realized that high-quality, low-cost, effective filter material is readily available; however, there is no current mask design that effectively seals the filter to a diversity of face sizes and shapes and allows for comfortable breathing and wearing over long periods. Nearly all disposable and cloth masks leave gaps between the face and mask edges. For large faces, they may be too tight to be comfortable and for small faces they may be too loose to be effective.

ULTRA FIT™ Innovations

Katharos Labs’ patent-pending solution uses malleable wires ultrasonically secured around the mask periphery, as well as an inward-facing flap to trap coughs, sneezes and normal exhalations. These features allow the ULTRA FIT mask to form to the shape and provide a close seal for virtually any face. An additional important element of any face mask is to make sure the mask is firmly, but not excessively pressed against the front of the face to maintain a good seal.  Although this may be accomplished by auxiliary ear loop length adjusters, the ULTRA FIT design provides two adjusters as an integral part of the mask body, so users won't need to carry around or fumble with the assembly of separate adjusters to assure proper mask pressure. These features, along with a highly effective particle and microbe filter comprising the mask body, have been scientifically studied using a variety of techniques and shown that Katharos Labs' design improves upon conventional rectangular surgical masks to significantly reduce unfiltered air penetration into and out of the mask.

ULTRA FIT Feature Chart

Four-Layer Filter Body - The ULTRA FIT mask utilizes a three-layer filter as well as a fourth-layer cough flap (described below) as part of the main mask body. The outer filter layer is a spunbond polypropylene material with excellent fluid resistance. The center layer is a electrostatically charged melt blown polypropylene layer for trapping particles, aerosols and droplets. The inner filter layer is a spunbond polypropylene material with a soft feel for increased comfort.

High Breathability - The "gold standard" for high performance disposable masks are N95-designated respirators. Although properly fitted N95 respirators provide excellent protection from particle infiltration, they have a significant down side: they become uncomfortable and difficult to breathe through during long wearing periods. The ULTRA FIT mask is unique, as it both provides a protection from airborne particles approaching that of N95 respirators, but is easy to breathe through (see ASTM F3502-21 testing breathability data here) and comfortable over long wearing periods.

Click hMask Comparison Chartere to see a chart comparing breathability and other features of various masks and respirators.


Extra Long, Unique Nose Wire - The mask incorporates a moldable wire across its top edge that extends nearly all the way to the corners. The properties of the wires on the mask have been carefully formulated to allow them to maintain their molded shape with reduced spring back. Conventional wires used in most other masks have a greater tendency to spring back after they have been formed to nose and face contours. The longer length and reduced spring back as well as the extra flap layer are important features for sealing the entire upper edge to not only reduce leakage, but to virtually eliminate fogging of glasses. Although shorter nose wires in conventional masks can form to the shape of the center portion of a nose bridge, a wire that extends to the corners both makes a more complete seal and increases the overall stiffness of the top edge because its ends are more securely anchored to the face by the nearby elastics.

Foldable Side Wires - This unique ULTRA FIT feature allows the sides of the mask to be effectively shortened to better fit smaller faces. In combination with the inner cough-trapping flaps, the folded side wires still provide an effective cheek seal, while forming a better mask shape for smaller faces, including children.

Pinchable Chin Wire - A stiff, bendable wire along the bottom of the masks provides a way for users with larger faces to pinch and fold over the center of the bottom mask edge to tighten the mask periphery to their face.

Integrated Ear Loop Length Adjusters - Two flat length adjusters are securely welded to the upper two corners of the mask exterior to allow the ear loop elastic lengths to be shortened. Users simply loop the elastics around the hooks, don the mask, then lengthen or shorten the elastics for a comfortable and secure fit.

Cough-Trapping Flaps ULTRA FIT masks incorporate a fourth layer of material to form four flaps, one along each edge, to help contain exhalations from escaping without passing through the main filter. During coughs, sneezes or normal exhalations, the flaps essentially inflate like a balloons to press against the face to better seal against escaping particles. This increases the amount of outgoing air that is forced to pass through the main filter of the mask.

Video Instructions - Each ULTRA FIT mask is individually wrapped with a transparent wrapper that includes a scannable QR code. Scanning this code with a phone or tablet camera opens a website, www.katharos.info, that shows a video demonstration of how to properly don and adjust an ULTRA FIT ™ mask.

Buy ULTRA FIT™ masks here.

The Science Behind the Mask

Most face masks in use today inherited their design from either 1) industrial applications, where their main function was excluding dust from a user's respiratory system, or 2) medical applications, where masks were primarily used in hospital settings. Katharos Labs redesigned the face mask for community use, to help keep people safe during a pandemic. A number of advanced instrumentation systems were utilized during the design process, allowing for simultaneous validation and design iteration.

Validation and Testing

The company has tested masks on a variety of subjects using Schlieren and laser-scatter video imaging, FLIR temperature imaging and Fit Factor/Leakage measurements with a TSI PortaCount 8038 (industry standard instrument for measuring mask fit). In addition, a qualitative survey was done with volunteers to evaluate the comfort level of the mask. The mask has also been tested by an accredited laboratory (SGS IBR Labs) and meets the ASTM F3502-21 specification. The test results for the ULTRA FIT ™ mask gave a level 2 filtration (95%) rating and level 1 breathability rating.

A number of scientific testing results are shown below as well as in the published PLOS ONE article here.

Schlieren Photography

Shlieren Photography uses variations in the refractive index of air caused by density gradients to distort a projected collimated light beam against a concave reflector, thereby creating a spatial variation in the light's intensity. This may then be visualized directly with a shadowgraph video.

Comparisons of subject exhalations between an ULTRA FIT mask and a conventional surgical-style mask show the ULTRA FIT mask periphery-molding and cough-flap features are able to trap air jets in the infraorbital region adjacent to the nose.  Thus, the conventional mask can have significantly more leakage in this region which can fog glasses and spread unfiltered exhaled air.

Schlieren ULTRA FIT comparison

The video on the left shows exhaled air exiting the ULTRA FIT mask at a slow velocity after being filtered across the entire mask surface. Note that heated expiratory air as well as ambient air adjacent to the face tends to rise.

The video on the right shows exhaled air exiting a conventional mask. Here a high velocity jet of air may be seen coming from the top edge of the mask at the initiation of expiration.  This air has essentially leaked from the mask without undergoing filtration.

It should be noted that Shlieren techniques can only capture air flows in two dimensions. Any leakage from other areas of a mask that are not visible from a profile view, for example past the cheeks, cannot be seen with this method.

Laser Scatter Imaging

Using extremely fine smoke particles allows us to follow air current traces in both conventional masks and the ULTRA FIT mask when illuminated by a collimated light source like a laser via light scattering. The video below shows a subject exhaling after breathing in smoke from a vaping device. On the left is a video of expirations with a conventional mask and on the right is the expiration of a similar volume of smoke while wearing an ULTRA FIT mask.

The left video shows a significant portion of the expelled air escaping through gaps in a conventional mask, resulting in air from the subject jetting out from the mask without being filtered. On the right, the amount of air escaping the ULTRA FIT mask without passing through he filter is minimal.

Laser Scatter Histograms

The magnitude of the difference in leakage during exhalations between a conventional mask and the ULTRA FIT™ mask may be estimated by counting the number of green pixels binned by intensity in a selected region. The chart shows a histogram of the number of pixels for various green pixel brightness values in the region just above the top edge of the masks in a single video frame for each side-view video.

FLIR Thermography

Thermal imaging of Ultra Fit mask

Forward Looking Infrared (FLIR) thermography is capable of remotely measuring variations in temperature, since the amount of radiation emitted by an object increases with temperature. Thermal imaging was used to measure temperature changes across masks during the inhalation of cooler air and the exhalation of warmer air. Testing was performed in a relatively cool 20oC room to analyze and compare the temperature dynamics on the mask surfaces during normal breathing through the nose. During inhalation, a cold region on the mask surface was restricted near the filtering region and had a clear boundary around the periphery of the ULTRA FIT. Whereas, with a conventional surgical mask, a cold region extended to the edges next to the nose and to the cheek ends of the mask. These show that even during inhalation, negative pressure changes in the mask cavity, the conventional mask made an inadequate face seal against the face. Whereas the ULTRA FITmask made a better contact to the face, indicating a less inward leakage. During exhalation, much higher surface temperature was observed with the ULTRA FIT mask at approximately 31.5°C, since more warm exhaled breath passed through the filtering region. In the case with conventional mask, the overall surface temperature of the filtering region was 28.5°C, much colder than that with the ULTRA FIT mask. Also, the edges on the cheeks of the conventional mask stayed relatively cold, suggesting that escaping warm breath did not provoke thermal conduction due to large openings at the cheeks.

ULTRA FIT Thermography histogram

The chart shows a histogram of the measured temperature for each thermogram pixel in the mask region during exhalations. Significantly warmer ULTRA FITcentral-mask temperature suggests that the flow of air is restricted through the filtering region of ULTRA FIT mask, whereas when the conventional mask is used, exhaled air has more leak paths that circumvent the filter, thereby exhibiting a lower central-mask temperature.

Fit/Leakage Testing

A PortaCount 8038 in "N95 Companion" mode was used to fit test several types of masks on about a dozen subjects. The PortaCount instrument is an industry standard device that can count the number of particles inside of a mas compared with the number of particles in the surrounding ambient air. The ratio of ambient particles per cubic centimeter versus internal mask particles per cubic centimeter is the "fit factor". The inverse of the fit factor is the leakage percentage.

Experience Users Fit Test Results

Although the ULTRA FIT™ mask is intuitive and straightforward to use, the fit testing measurements showed that experienced users had better results with the masks as compared to novice users. Experienced users seemed to be better at molding the masks to their particular facial features where leaks were more likely to occur. Results showed that these users had about a 10X reduction in leaked particles that escaped the main filter of the mask as compared to a conventional surgical mask. ULTRA FIT™ masks were able to filter about 95% of particles as compared to ambient particle density. The best particle filtration/fit results for an experienced user was about 98%, which approaches levels of well-fit N95 masks and surpasses levels of N95 respirators that are not properly fitted.

Leakage for Noice Users
Since no special training was given to the subjects, the fit test results for novice users varied more and had higher leakage rates than those for experienced users. In addition, subjects with facial hair generally have poorer results for all masks tested. Only users without facial hair are shown here. In this test, ULTRA FIT™ masks were compared to both conventional surgical masks and conventional KF-94 masks. The ULTRA FIT™ masks showed significant improvement in sealing (by about a factor of 3X), reducing the number of particles that escaped  the main filter of the mask.

Qualitative Comfort Testing

Ultra Fit mask comfort chart

In order to assess comfort of wearing an ULTRA FIT™ mask compared to other disposable masks, we conducted an online survey with 15 participants after providing them with both conventional surgical masks and ULTRA FIT™ masks. The demographics of the participants were varied by sex, age, and ethnicity. Based on the questionnaires, most participants responded that the ULTRA FIT™ masks were easier or similar in difficulty to don compared to conventional masks, with only 13% responding more difficult when donning the ULTRA FIT™ masks. 94% of the respondents found the ULTRA FIT™ masks more comfortable or similar in comfort to surgical masks. Finally, most responded that they use disposable face masks (surgical style masks).