The lignin yield increases with P-factor and temperature, with a predicted maximum yield of 98 ± 13% at (P f , T ) = (2500, 207 • C) . We explain the relation between yield and P-factor by an increased cleavage of interunit lignin and lignin-carbohydrate linkages and the formation of more acetone-soluble lignin fragments, under more severe reaction conditions. We note that the experimentally measured lignin yield of 108% at (P f , T ) = (2500, 210 • C) exceeds the theoretically predicted maximum yield but is still contained within one standard deviation of the prediction. The measured value is furthermore larger than the theoretical value of 100 mass%, indicating the formation of polyfurans from xylan degradation products (furfural) that is quantified as lignin (so-called pseudo-lignin) .