The proposed SwissFEL will provide both hard x-rays down to 1Å and soft x-rays with full polarization control at the rather small maximum electron energy of 5.8GeV. This continues the strategy of the medium energy synchrotron facilities, namely the SLS. The U₁₅ and UE40 undulators are based on the experience with small period, small gap in-vacuum undulators and of APPLE II type respectively but are optimized for FEL operation. The undulator design including room temperature versus cryogenic principle, field optimization, materials and the demands for a series production will be discussed.