C18 vs C20

C20 and C18 are about equally stiff. Their densities are about the same. Per unit mass they are about equally stiff (23.68 and 23.75 MJ/kg). Strength: f_m,k = 18 MPa for C18, f_m,k = 20 MPa for C20.

C18 EN 338:2016 C20 EN 338:2016

Side by side

ratio = C20 / C18 · log scale

Property	C18	C20	Unit	Ratio
E₁ Modulus, direction 1	9	9.5	GPa	1.06×
E₂ Modulus, direction 2	0.3	0.32	GPa	1.07×
E₃ Modulus, direction 3	0.3	0.32	GPa	1.07×
G₁₂ Shear modulus 1-2	0.56	0.59	GPa	1.05×
G₁₃ Shear modulus 1-3	0.56	0.59	GPa	1.05×
E₀,₀₅ Modulus parallel to grain, 5 % fractile	6	6.4	GPa	1.07×
ρ Density	380	400	kg/m³	1.05×
ρ_k Density, characteristic (5 % fractile)	320	330	kg/m³	1.03×
f_m,k Bending strength	18	20	MPa	1.11×
f_t,0,k Tension parallel to grain	10	11.5	MPa	1.15×
f_t,90,k Tension perpendicular to grain	0.4	0.4	MPa	1×
f_c,0,k Compression parallel to grain	18	19	MPa	1.06×
f_c,90,k Compression perpendicular to grain	2.2	2.3	MPa	1.05×
f_v,k Shear strength	3.4	3.6	MPa	1.06×
E/ρ Specific stiffness E/ρ · derived	23.68	23.75	MJ/kg	1×
c₀ Bar wave speed √(E/ρ) · derived	4867	4873	m/s	1×
f/ρ Specific strength f/ρ · derived	47.37	50	kJ/kg	1.06×

Values at the first thickness band or product form of each material (EN 338:2016; EN 338:2016). A minimum and a characteristic value are not the same kind of number — read the ratio as a guide. Each material's page lists every band and every source.