One physical quantity
Specific resistance is the pressure drop divided by the flow that produced it. It is measured on a constant-flow bench, on a new device, and it does not depend on the flow chosen for the test.
XRS™ scale · technical reference XRS 001:2026
How long can this mask be breathed comfortably?
Standards cap the breathing resistance of a mask; none grades it. The XRS scale turns one bench measurement — specific resistance — into six levels, X1 to X6, each with a breathing endurance a buyer can read on the pack and compare between brands.
- XRS 001:2026 · first edition
- CC BY-ND 4.0
- Heuristic — not a standard
The six levels
Specific resistance Rs in Pa/(L·s⁻¹), measured on a new respirator. Breathing endurance is what the resistance permits — always within the manufacturer's stated conditions of use.
Rs = Δp / Q
One input quantity, invariant with flow to better than ± 11 % on the normative values
15 / 15
Independent published markers that fall into the scale without a single inversion
200 ≈ 208 ≈ 218
The X5/X6 boundary, set from filtration ceilings, coincides with the ISO 16976-4 physiological limits within 10 %
8
Refutation conditions stated in advance — the scale says what would invalidate it
What the scale is
A measure, not a verdict.
Every level is a good level for some use. A mask at X5 is the right choice for a short task in a loaded atmosphere; a mask at X1 is the right choice for a child or for sleep. The scale reports a position on an axis — it does not rank products as good or bad.
Six anchored thresholds
30, 60, 100, 140 and 200 Pa/(L·s⁻¹). None is set by convention: the central boundary is the psychophysical detection threshold of added inspiratory resistance, the upper ones are the resistance ceilings of the filtration classes.
Two independent dimensions
The XRS level qualifies breathing comfort. It says nothing about filtration efficiency, and it never appears next to a protection class in the same block. A mask can be X2 and highly filtering, or X5 and poorly filtering.
Who it is for
One scale, four readers.
Wearers
Scan the code on the pack, or open the page of the level: what the level means, how long the resistance permits, and what the level does not say.
Level pages X1 to X6Buyers and safety officers
Two FFP2 masks that both comply can differ by a factor of three in resistance. The level gives an opposable criterion, expressed in the unit of the decision: the wearing duration that is actually sustainable.
Use profiles and tablesManufacturers
Lowering the pressure drop of a compliant product is invisible on a pack today. The XRS marking turns a test-report line into a shelf argument — under a licence with quality control and a public register.
Licence and price listScientists and laboratories
The construction, the fifteen-marker consistency test, the ISO 16976-4 conformity check and the pre-registered validation protocol are published in full. The scale is falsifiable by design, and it invites contradiction.
Method, evidence and limits
On the pack
Read it in three moves.
The XRS panel is the same object on every licensed product, at the same dimensions, so that three boxes of three brands compare on the shelf without reading a word.
- The positionSix cells, one lit. The scale bar is the comparative element: it reads in one colour, in photocopy, and for a colour-blind reader.
- The durationUnder the mandatory heading BREATHING ENDURANCE, the normative short mention of the level — never paraphrased — and the comfort qualification.
- The boundary and the reference"New respirator · Within the manufacturer's stated conditions of use", then the logotype and the code that leads to the page of the level on this site.
Economic model
The reference is free. The mark is licensed. The control is funded.
Anyone may read, cite, redistribute and apply XRS 001:2026, in design as in research, without asking. Printing "XRS level X2" on a product requires a licence, because a mark without effective quality control means nothing — and, in several jurisdictions, ceases to exist.
Public, uniform price list
Set at the full cost of instruction and surveillance with a 15 % safety margin and no profit on the declaration right. Identical for every applicant; degressive on an objective criterion only.
Three regimes, one register
Controlled self-declaration, third-party test, or XALPES certification. Whatever the regime, every declaration is instructed, entered in the public register and monitored.
Seeding programme until 31 December 2027
The declaration right is waived for every declaration registered before that date, and for research, teaching and scientific publication at any time. Only the test is invoiced.
XRS 001:2026 is a proprietary technical reference published under the sole responsibility of XALPES LLC. It is not a standard, has no regulatory value, does not classify filtration efficiency and does not authorize any regulated use. The human-panel validation described in its Clause 14 has not yet been conducted; its success criteria and its refutation conditions are published in advance. The reference is open to comment.