The thermal conductivity (λ) of wood shavings insulation mats was investigated in terms of wood shavings' dimensions and mat density. The raw materials were collected from at imber-precut factory and three fractions，L，M，and S with different dimensions and thickness were obtained by a sieve classification. The bulk density of L and M was almost identical.In order to investigate the effects of raw material size on mat thermal conductivity， the λ of mats with a density of 140kg/m3 was compared among L，M, and S fractions. It was found that the λ of M fraction mats (M-mats) was about 12% lower than that of L fraction mats (L-mats). In order to investigate the effects of mat density，the λ of mats with a density of 120 and 180kg/m3 was also measured for L-mats and M-mats. The results showed that the higher mat densities were，the lower the λ became. Also，the λ of M-mats was found to be 11% lower than that of L-mats on average through this density range.To quantitate the effects of raw material size on mat thermal conductivity，we calculated the apparent λ of coarse pores in the mats (λvl)，which includes the effects of convective and radiant heat transfer that were calculated with the use of a mix law of two types of layer arrangement models parallel (PA-model) and perpendicular (PE-model) to the direction of heat flow. The results showed that the λvl of M-mats was 27% lower than that of L-mats on average. This suggests that using smaller wood shavings makes coarse pores smaller. which consequently inhibits convective and radiant heat transfer. Also，the results revealed that the existence ratio of the PA-model was much smaller than the PE-model. Since changes in λvl affect only the PA-model, reductions in mat thermal conductivity smaller than in λvl are explicable by the low existence ratio of the PA-model.