APP	Ammonium polyphosphate
ATH	Aluminum hydroxide
ATR-FTIR	Fourier transform infrared spectroscopy
av-HRR	Average of heat release rate
CS	Compressive set
DPS	Degree of phase separation
DSC	Differential scanning calorimetry
TA	Thermal analyses
DTG	Derivative thermogravimetry
EG	Expandable graphite
F	Fyrol pn
FPUF	Flexible polyurethane foam
FR	Flame retardant
FTIR	Spectrophotometric analyses
HRR	Heat release rate
HS	Rigid segments in polyurethanes
HSe	Rigid segments in polyurethanes determined from tga analysis
HSt	Rigid segments in polyurethanes for theoretical foam
K	Keratin filler
ma1, ma2, ma3	Weight loss at each of the degradation stages in air atmosphere
MDI	Diisocyanate ongronate 4040—a mixture of monomeric isomers and oligomer icmethylenediphenyl-4, 4′-diisocyanate
mn1, mn2, mn3	Weight loss at each of the degradation stages in nitrogen atmosphere
MTH	Magnesium hydroxide
pHRR	Maximum value of heat release rate
pHRR/tPHRR	pHRR ratio at the time of its achievement, maximum value of heat release rate
PML	Percentage mass loss
R	Hydrogen bonding inde
Ra900	Residue after degradation at 900 °c in air atmosphere
Rn900	Residue after degradation at 900 °c in nitrogen atmosphere
SAG	Comfort coefficient
SEM	Scanning Electron Microscope
SS	Flexible segments in polyurethanes
SSe	Flexible segments in polyurethanes determined from TGA analysis
SSt	Flexible segments in polyurethanes for theoretical foam
Ta1, Ta2, Ta3	Temperature of the maximum degree of degradation in air atmosphere
Ta5%	Temperature of 5% weight loss in air atmosphere
Tg	Glass transition temperature
TGA	Thermogravimetric Analyses
Tgs1, Tgs2	Glass transition temperature in the first and second heating cycle
THR	Total heat release
Tn1, Tn2, Tn3	Temperature of the maximum degree of degradation in nitrogen atmosphere
Tn5%	Temperature of 5% weight loss in nitrogen atmosphere
Tt	Temperature of the transformation disorder-order
Va1, Va2, Va3	Maximum rate of degradation in air atmosphere
VE	Unmodified polyurethane foams
VEPUR	Viscoelastic polyurethane foam
VE+ 10 K	Unmodified polyurethane foam with addition of 10% keratin
VE + 10 K +5 F	Unmodified polyurethane foam with addition of 10% keratin and 5% Fyrol
VE + 10 K +10 ATH	Unmodified polyurethane foam with addition of 10% keratin, 10% aluminum hydroxide
VE + 10 K+ 10 ATH+5 F	Unmodified polyurethane foam with addition of 10% keratin, 10% aluminum hydroxide and 5% fyrol
VE + 10 K +10 MTH	10% magnesium hydroxide
VE + 10 K +10 MTH + 5 F	Unmodified polyurethane foam with addition of 10% keratin, 10% magnesium hydroxide and 5% fyrol
VE + 10 K +10 ZO	Unmodified polyurethane foam with addition of 10% keratin and 10% zinc oxide
VE + 10 K +10 ZO +5 F	Unmodified polyurethane foam with addition of 10% keratin, 10% zinc oxide, and 5% fyrol
VE + 10 K +10 EG	Unmodified polyurethane foam with addition of 10% keratin and 10% expandable graphite
VE + 10 K +10 EG +5 F	Unmodified polyurethane foam with addition of 10% keratin 10% expandable grophite and 5% fyrol
VE + 10 K +10 APP	Unmodified polyurethane foam with addition of 10% keratin and 10% ammonium polyphosphate
VE + 10 K +10 APP +5 F	unmodified polyurethane foam with addition of 10% keratin, 10% ammonium polyphosphate, and 5% fyrol
Vn1, Vn2, Vn3	maximum rate of degradation in nitrogen atmosphere
ZO	zinc oxide
Δcp *	specific heat in the scope of glass transition transformation.
ΔHt	enthalpy of transformation disorder–order