The flexural properties and mass losses of thermal modified Douglas-fir pretreated with boron or glycerol were examined. Pretreatments were associated with slight, but not significant, reductions in modulus of rupture (MOR) and modulus of elasticity （MOE）of Douglas-fir at different thermal treatment levels. Boron pretreatment had the greatest effect on MOR. MOR of non-pretreated and boron treated samples increased slightly at the initial stage of thermal treatment and then decreased with rising temperature and time. The MOR of glycerol treated samples decreased with increasing temperature and time. The thermal treatments employed had no significant effect on MOE. Further studies are underway to characterize the durability of these materials.

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