The purpose of this work was to test the effect of different polymer coating materials on water uptake (imbibition and water vapour uptake) and germination performance before and after storage of onion seeds. Coating the seeds with hydrophobic polymers especially LS (linseed oil), PE (polyethylene), PVDC-1 (Daran 8600C) and VA (Vinamul 3240) reduced imbibition, but only PVDC-2 (Daran SL112) significantly reduced water vapour uptake. LS, PE and VA coatings significantly reduced germination before and after storage in 85% RH for 10 weeks at 25 degrees C. These polymers formed a hard film which appeared to form a physical barrier to primary root protrusion. Moisture contents after storage of untreated and coated seed were similar (between 13.0 and 13.3%), indicating that no coatings reduced water vapour uptake in storage. Guidelines for an appropriate experimental approach in the search for effective coatings to reduce water vapour uptake and increase storage life are discussed. (C) 2009 Elsevier B.V. All rights reserved.