Battery separators are characterized largely by their material and by their shape. In this paper options to achieve optimization of polyethylene separator properties are discussed, based on reasonable variations in material and shape, in particular with respect to electrical resistance and chemical stability. The raw materials of polyethylene separators, i.e. silica, ultrahigh-molecular weight polyethylene, mineral oil and some additives are presented, their relative amounts are varied, and the resulting properties are evaluated with regard to oxidation stability, deposits generated, puncture strength, and electrical resistance. Distinct consideration must be given to the dimensional parameters of both the separator sheet and the distance-setting ribs. Various proposals, in particular for the latter, are referred to in the literature without critical evaluation of their effect on battery performance. Some considerations for optimized profile design and initial battery results are reported. (C) 2001 Elsevier Science B.V. All rights reserved.