These devices are used to freeze substitute vitrified biological samples. Freeze Substitution is a process in which the water molecules within the samples are exchanged with a solvent (usually acetone), then, the solvent with a resin (Epon or Lowicryl resins). In the end, the sample is fully infiltrated with pure resin. Polymerisation of the resin is performed outside (case with Epon resin) or inside the machine when using Lowicryl. This latter resin is polymerised under a UV lamp, starting at -45ºC, then gradually moving up to RT (case with Lowicryl HM20). At the end of the process hard plastic blocks are generated ready to be cut by ultramicrotomy.