Definitions of measured and dimensionless variables and numerical values of bulk material variables used in the dimensional analysis.

Property	Measured variables	Dimensionless variables
Thermal Conductivity (k)	k f ≡ foam k
	k b ≡ bulk material k
	k cellulose = 0.23 W m−1 K−1 (ref. 125)
	k PU = 0.19 W m−1 K−1 (ref. 126)
	k PLA = 0.18 W m−1 K−1 (ref. 127)
Density (ρ)	ρ f ≡ foam apparent ρ
	ρ b ≡ bulk material ρ
	ρ cellulose = 1500 kg m−3 (ref. 128)	Expansion ratio ≡ θ = 1/ρrel
	ρ PU = 1225 kg m−3 (ref. 126)	Void fraction ≡ γ = 1 − ρrel
	ρ PLA = 1240 kg m−3 (ref. 129)
Average cell size (d)	d ≡ measured average cell size
	d max ≡ max cell size in 1 m3 at given γ