At the pseudoeutectic, the polymer structurein the crystalline region shifts from a P(3HB) type crys-tal (fiber repeat 0.596 nm), to a P(3HV) crystal one (fiberrepeat of 0.556 nm) (by XRD), with the middle region orig-inally being supposed to have both crystal types present[190]; however later work [201] showed that this was dueto blends being present. It was originally proposed that the3HV units could sit in the P(3HB) crystal without distortingthe crystalline structure or lattice significantly, and like-wise for the HB units in the HV crystal. However, solutiongrown single crystals of P(3HB) and P(3HB-co-3HV) (up to30% HV) showed a linear increase in melting points and ahyperbolic increase in long spacings as the crystallizationtemperature increases [172f comonomer component and the other is in the