The high natural durability of western redcedar (WRC) heartwood is primarily attributed to the presence of extractives that are toxic to fungi. However, its durability may also come from its low equilibrium moisture content (EMC). Recently extractives were found to contribute to western redcedar heartwood's low EMC (Stirling and Morris, 2005). In the present study we sought to determine the degree to which certain groups of extractives contributed to this low EMC. The non-polar tropolones were found to have no effect on WRC's EMC. Lignans, where are abundant in WRC heartwood, were associated with its low EMC. In addition to the known extractives there are likely other differences in chemistry or structure that account for the low EMC of WRC.