Porous ultra-fine fibres were prepared via selective thermal degradation of electrospun polyetherimide/poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PEI/PHBV) fibres. Electrospun PEI/PHBV fibres had a relatively broad size distribution in the range of 2.6-15.1 mum. PEI and PHBV were partially miscible and phase separation proceeded rapidly during the electrospinning process. Most of the PHBV in PEI/PHBV fibres was degraded at 210 degreesC within 90 min, while PEI remained undegraded. PEI/PHBV(75/25) and PEI/PHBV(50/50) fibres showed highly porous surfaces after thermal degradation of PHBV at 210 degreesC. (C) 2004 Elsevier Ltd. All rights reserved.