It is reported earlier that, like halogens, phosphorus could also function as radical scavengers, improving the FR properties. Further research has revealed that phosphorus can form crosslinks, chars and aromatic structures when surrounded by oxygen-atom containing polymers. Since the effectivity of PFR additives depends very much on whether they are active in the condensed phase or in the gas phase, it was important for us to determine the distribution of Phosphorus in different phases. reported the synergistic and catalytic effects of FR additives on the flame retardancy of polymeric materials in an earlier study. To determine the distribution of P in different phases, we measured P contents for different samples for example we determined in the model HFFR compounds containing PFR, in the PFR additives that we used in our model formulations, and also in the residues that were left after pyrolyzing the model compounds in muffle oven as described above. Table summarizes the results. The distribution of P in the gas and condensed phases was calculated based on these values, and the results are summarized in Table below. The results show that estimations of P contents provide significant information regarding the activity of PFR, i.e., whether the used PFR acts as a char former or a radical quencher. Paxymer® presence in HFFR formulations enhances P-concentrations in the condensed phase, both in formulations BG457 and BG 455 for PFR 4 and PFR 2, suggesting that it initiates the formation of more char even at lower addition levels of PFR additives. The extent of char formation is higher for PFR 4 than for PFR 2. The formation of more char may be due to the presence of functional groups in Paxymer® which, as expected, should help to form more cross-links in the polymer matrix and thereby increasing char content and thereby improving fire resistance properties at lower dosage levels of PFR. We observed some intumescence in the residues after investigating them by scanning electron microscopy (SEM). The enhanced cross-linking also demonstrated that molten polymers do not drip when the formulations that contained Paxymer® were burnt. This is crucial for minimizing the pool fire, which is also one of the causes for flame spread. Paxymer® was shown to function as a good drip suppressant and could successfully be used to substitute halogenated non-dripping additive such as teflon® in a recent study . Seefeldt's PhD thesis demonstrated that Paxymer® acts as a powerful synergist for the flame retardation of wood polymer composite (WPC) materials.