A Shore hardness number and the force needed to close a door are not the same measurement. ASTM identifies D2240 as its durometer-hardness method and describes indentation under specified indenter conditions; ASTM D575 concerns compression-deflection behavior of certain rubber compounds, but its public scope explicitly excludes sponge rubber and hard rubber. The names and scopes are different, so a single hardness figure cannot be used as a substitute for an actual gasket compression/closure specification.
Look at the entire profile, not just its material label
Parker explains that the closure force of a hollow O-ring can be changed by its wall thickness without reducing the compound hardness. That is a concrete manufacturer example of geometry affecting force independently of the material's nominal hardness. It is not an interchangeability statement about a particular weatherstrip.
When inspecting a prospective replacement, write down separately: the label on the material datasheet; the bulb or hollow profile geometry actually depicted; the intended deformation/compression condition stated by its issuer; the carrier/retention interface; and any closure-force test tied to that exact profile. If the candidate offers only '70 Shore A' or a similar isolated number, leave the closing-force field as unknown. For a sponge-rubber bulb, do not presume D575 applies; request the manufacturer’s applicable method and exact profile/load-deflection evidence.
Two-column diagnostic worksheet
| Field shown in source | What you can conclude | What you cannot conclude |
|---|---|---|
| Shore type and material hardness | A named hardness test result exists | Exact closing force of an unknown hollow shape |
| Applicable compression-deflection test at stated conditions | A result for that material/specimen and method exists | Direct fit of a different profile |
| Hollow-wall specification | Profile geometry can be compared | Compatible groove or door alignment without system evidence |
| Door's actual closed position | Whether closure is operating normally | Which material formulation would perform best long-term |
Practical decision
If the installed replacement makes the door difficult to operate, do not solve the issue by shopping for an arbitrarily softer polymer. DOE's June 2024 checklist explicitly requires weatherstripping and sweep not to obstruct door operation. Record the contact pattern, manufacturer and retention style; separate a geometry mismatch from hardware alignment using the proper door instructions.
Buy / hold boundary: Only an issuer-confirmed profile and the opening's actual geometry can support fit. Hardness alone is a useful datasheet field but is not an approved substitute for an installation specification. No compression percent, safe maximum door force or universal ideal Shore number is provided by these sources.
Sources and references
— store.astm.org · ASTM D2240-15e1 public preview §4.1 · ASTM D2240-15e1 public preview §4.1 · https://store.astm.org/d2240-15e01.html— store.astm.org · ASTM D575-91(2024) public preview §§1.1,4.1 · ASTM D575-91(2024) public preview §§1.1,4.1 · https://store.astm.org/standards/d575— discover.parker.com · Parker hollow-O HTML wall-thickness force section · Parker hollow-O HTML wall-thickness force section · https://discover.parker.com/extruded-hollow-o-ring-seals— www.energy.gov · DOE/NREL June 2024 p2 checklist · DOE/NREL June 2024 p2 checklist · https://www.energy.gov/sites/default/files/2024-07/11-1_install-weatherstripping-on-exterior-door.pdf