<p>In the present paper, pinewood samples with varied thicknesses incorporating different additives, including fish gelatine, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), triphenylphosphine (TPP), diammonium phosphate ((NH₄)₂HPO₄) and sodium carbonate (Na₂CO₃) were investigated by using a cone calorimeter. The measured parameters included ignition time, mass loss rates (MLR), heat release rates (HRR) and yields of selected gaseous species. The results demonstrated that as the sample thickness increased, the deformation to the tested specimens were less pronounced. The treated samples with a thickness of 13&#xa0;mm exhibited intermediate properties to those of thermally thin and thermally thick materials. For samples with higher thickness, the second peak HRR was noticeably lower than the first. At a median heat flux of 50 kWm⁻², the treated samples exhibited a prolonged burning duration, possibly owing to the presence of flame-retardant additives. However, for the sample with thickness of 30&#xa0;mm, this effect was only nominal. The yields of CO₂ remained nearly constant across varying heat fluxes for both untreated and treated samples, indicating that the extent of the oxidation reactions is not influenced by the imposed heat flux. The results from present study, which primarily focused on flammability behaviours of pinewood with varied thicknesses warrants, further investigations with a view to deciphering the underlying mechanistic pathways of thermal degradation and flammability of the tested samples.</p>