A	specimen cross sectional area (flow resistivity measurement)
d	bar width
h	bar height
k	number of neighbors in KNN model
$k_0^{\prime }$	static thermal permeability
l	specimen height
q	volume flow through the specimen (flow resistivity measurement)
R	airflow resistance
R	coefficient of determination (performance measure of ML model training)
s	bar spacing
$\alpha$	absorption coefficient
${\alpha }_{\infty }$	tortuosity (high frequency limit)
$\Delta p$	pressure drop over the specimen (flow resistivity measurement)
$\mathsf{\Lambda }$	viscous characteristic length
${\mathsf{\Lambda }}^{\prime }$	thermal characteristic length
$\mathsf{\Xi }$	flow resistivity
$\rho$	Pearson’s Correlation Coefficient
$\phi$	plane angle
$\varphi$	porosity
AM	additive manufacturing
ANN	artificial neural network
DOE	design of experiment
JCAL	Johnson–Champoux–Allard–Lafarge
KNN	k-nearest neighbor
LHS	latin hypercube sampling
MEX	material extrusion
ML	machine learning
PBF-P	powder bed fusion of polymers
PET-G	glycol modified polyethylene terephthalate
PLA	polylactide
VAT	vat photopolymerization