Although boron has many advantages as a wood preservative, this chemical performs poorly in leaching exposures. In this study, we investigated the potential for decreasing the leachability of boron preservatives with polyethylene glycol (PEG). Southern pine (Pinus spp.) test samples impregnated with combinations of sodium borate or boric acid and PEG were subjected to both leaching and decay tests. Samples treated sequentially with sodium borate or boric acid and then with PEG-400 or PEG-600 showed a significantly increased resistance to boron leaching. However, decay tests indicated that blocks treated with sodium borate or boric acid and PEG experienced slightly higher weight losses at nearly all retention levels, possibly as a result of PEG depletion. Thus, although the results suggest that bulking agents may enhance the resistance of boron to leaching, the enhanced leach resistance may be a temporary effect.