Symbols and Abbreviations	Meanings	Units
<…>	– distinguishing symbol for a physical quantity averaged over thickness range
A	– “white” (pure) EPS product, tested herein or elsewhere in literature
B	– “dotted” EPS product, tested herein
dotted	– “dotted” EPS product, tested elsewhere [42]
C	– “grey” EPS product, tested herein
grey	– “grey” EPS product, tested elsewhere [42]
𝒞	– correction parameter (Table 1)	(W·m−1·K−1)
CEN	– European Committee for Standardization
DSC	– differential scanning calorimetry
TGA	– thermogravimetric analysis
d	– thickness (height) of the panel or sample	(m)
dA, dB, dC	– thickness of the panel or sample referring to product A, B, or C, respectively
d max	– maximum permissible thickness of the sample assigned to the chamber of specified dimensions of the plate instrument	(m)
d min	– minimum permissible thickness of the sample assigned to the chamber of specified dimensions of the plate instrument	(m)
d L	– the panel thickness limit of the R′ and λ′ (non-)linearity	(m)
dLA, dLB, dLC	– the thickness limit referring to product A, B, or C, respectively
EPS/XPS	– expanded/extruded polystyrene
GFMs	– gas-filled materials
GHP	– guarded hot plate instrument
GMP	– graphite microparticles
HFM	– heat flow meter instrument
k	– coverage factor used in statistical analysis
L	– thickness effect parameter
µ-RS	– micro-Raman spectroscopy
m	– measured mass	(kg)
NIMs	– nanoinsulation materials
PCMs	– phase change materials
PhF	– phenolic foam
PIR	– polyisocyanurate
PS	– polystyrene
PUR	– polyurethane
q	– density of heat flux through an insulation panel	(W·m−2)
R 0	– extrapolated thermal resistance corresponding to panel thickness d = 0, in particular referring to product A, B, or C, respectively (after correction)	(m2·K·W−1)
R0A, R0B, R0C
R′0	– extrapolated thermal resistance corresponding to panel thickness d = 0, in particular referring to product A, B, or C, respectively (before correction)	(m2·K·W−1)
R′0A, R′0B, R′0C
R	– corrected thermal resistance (obtained by converging the corrected λ for a given panel thickness d)	(m2·K·W−1)
RA, RB, RC	– corrected thermal resistances referring to product A, B, or C, respectively
R′	– apparent thermal resistance (as measured for a given panel thickness d)	(m2·K·W−1)
R′A, R′B, R′C	– apparent thermal resistance referring to product A, B, or C, respectively
R D	– declared thermal resistance at Tm = 10 °C (assigned by a manufacturer to each panel of thickness d)	(m2·K·W−1)
RDA, RDB, RDC	– declared thermal resistance referring to product A, B, or C, respectively
SIMs	– super insulating materials
SRM	– standard reference material
TDS	– technical data sheet provided by the manufacturer
T cm	– crystalline melting temperature	(°C)
T g	– glass transition temperature	(°C)
T m	– average measurement (test) temperature	(°C)
U-value	– thermal transmittance (overall heat transfer coefficient)	(W·m−2·K−1)
VIMs	– vacuum insulation materials
x, y	– panel dimensions: length, width	(m)
ΔT	– temperature difference between the “hot” and “cold” plates	(°C)
λ	– corrected thermal conductivity coefficient (resulted after correction of λ′ for a given panel of thickness d)	(W·m−1·K−1)
λA, λB, λC	– corrected thermal conductivity coefficient referring to product A, B, or C, respectively
λ′	– apparent thermal conductivity coefficient (as measured without Al-foil for a given panel thickness d)	(W·m−1·K−1)
λ′A, λ′B, λ′C, λ′dotted, λ′grey	– apparent thermal conductivity coefficient for a given product (as measured without Al-foil)
λ″	– apparent thermal conductivity coefficient (as simulated or measured with Al-foil for a given panel thickness d)
λ″A, λ″B, λ″C, λ″dotted, λ″grey	– apparent thermal conductivity coefficient for a given product (as simulated or measured with Al-foil)
λ D	– thermal conductivity coefficient at Tm = 10 °C, as declared by a manufacturer (independent on thickness d)	(W·m−1·K−1)
λDA, λDB, λDC	– declared thermal conductivity coefficient referring to product A, B, or C, respectively
λ C SRM	– SRM thermal conductivity coefficient (given in the Certificate for Tm = 10 °C)	(W·m−1·K−1)
λ M SRM	– SRM thermal conductivity coefficient (measured with HFM FOX 600 at Tm = 10 °C)	(W·m−1·K−1)
λ t	– thermal transmissivity, horizontal asymptote of λ(d), reciprocal gradient of the R(d) linear fit (after correction)	(W·m−1·K−1)
λtA, λtB, λtC	– thermal transmissivity, referring to product A, B, or C, respectively
λ′t	– thermal transmissivity, horizontal asymptote of λ′(d), reciprocal gradient of the R′(d) oblique asymptote (before correction)	(W·m−1·K−1)
λ′tA, λ′tB, λ′tC	– thermal transmissivity referring to product A, B, or C, respectively
ρ	– bulk density of polymeric insulation material (very low or low)	(kg·m−3)
ρA, ρB, ρC	– bulk density value of product A, B, or C, respectively
ℑ	– heat transfer factor, the effective conductivity coefficient (Supplementary Material part 1)	(W·m−1·K−1)
ℑA, ℑB, ℑC	– heat transfer factor referring to product A, B, or C, respectively
Uncertainty
Δ	– absolute error, accuracy or absolute change of a quantity
U(𝒞)	– expanded uncertainty of the correction parameter in the calculation of 𝒞	(W·m−1·K−1)
U(d)	– expanded uncertainty of the sample thickness measurement in HFM FOX 600	(m)
U(L)	– expanded uncertainty of the thickness effect parameter calculation
U(m)	– expanded uncertainty of the mass measurement	(kg)
U(q)	– expanded uncertainty of the heat flux density measurement	(W·m−2)
U(x) or U(y)	– expanded uncertainty of the x, y dimensions measurement	(m)
U(ΔT)	– expanded uncertainty of the temperature difference measurement	(°C)
U(λ)	– expanded uncertainty in determination of the thermal conductivity coefficient λ	(W·m−1·K−1)
U(λ′)	– expanded uncertainty in measurement of the thermal conductivity coefficient λ′	(W·m−1·K−1)
U(λ)/λ	– relative expanded uncertainty in determination of the thermal conductivity coefficient λ	(%)
U(λ′)/λ′	– relative expanded uncertainty in measurement of the thermal conductivity coefficient λ′	(%)
U(λCSRM)	– expanded uncertainty in determination of the SRM thermal conductivity coefficient λCSRM (given in the Certificate for Tm = 10 °C)	(W·m−1·K−1)
U(λMSRM)	– expanded uncertainty in measurement of the SRM thermal conductivity coefficient λMSRM (measured with HFM FOX 600 at Tm = 10 °C)	(W·m−1·K−1)
U(ρ)	– expanded uncertainty of the bulk density measurement	(kg·m−3)
U(ρ)/ρ	– relative expanded uncertainty of the bulk density measurement	(%)
σ	– standard deviation