Density, compression set, and support factor (IFD ratio) calculators for flexible cellular urethane foam (ASTM D3574, IS 7888)
◉ ASTM D3574-03, IS 7888:1977 (R2019) STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. D3574 and IS 7888 use genuinely different compression set conventions: D3574 offers two methods (Ct, referenced to original thickness; Cd, referenced to spacer/deflection), while IS 7888 always references original height regardless of deflection level (50/75/90%) — the two aren't directly interchangeable without knowing which convention a given specification calls for.
Identification
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Density (ASTM D3574 Test A / IS 7888 §4)
Density = (M/V) × 106, kg/m³ (D3574 Eq 1; IS 7888 §4 is the same relationship). Core density: specimen ≥1000mm³, free of skin, cut away from voids/defects. Section density: full-thickness specimen with skins, ≥0.1m² area.
Result
Density—
Compression Set
D3574: Ct = [(to−tf)/to]×100 (Eq 2, preferred when unspecified); Cd = [(to−tf)/(to−ts)]×100 (Eq 3). Approximate Ct→Cd conversion: multiply 50% Ct by 2, 75% Ct by 1.33, 90% Ct by 1.11. IS 7888: same formula shape as Ct at whichever deflection (50/75/90%) was tested, always referenced to original height — average of 3 specimens shall be reported.
Result
Compression set—
Indentation Force Deflection & Support Factor (ASTM D3574 Test B)
Support Factor = 65% IFD / 25% IFD — a comfort/firmness-progression metric (higher generally means the foam resists "bottoming out" better). Standard indentor: 203mm flat circular foot, 4.5N contact force, deflect at 50±5mm/min, read force after 60±3s dwell at each level.
Result
Support Factor—
Shear Fatigue Test (IS 7888 §7)
Fl = [(L0−Lt)/L0]×100 (§7.4.1); Ft = [(t0−tt)/t0]×100 (§7.4.2). Per the standard's own validity rule, percentage loss in load deflection is only to be reported if the percentage loss in thickness is less than 10%.