It could be that the wire supplied in the kits varies depending on availability etc.. But, my Crack kit came with Carol 20 awg solid core with PVC insulation. This wire is made by General Cable and I buy it from Digikey. Super easy to work with IMHO.
http://parts.digikey.com/uk/1/6450-green-20awg-hookup-wire-solid-c2118-12-06.html