In order to keep the liquid xenon inside XENON1T at a temperature of almost -100°C, the TPC is installed inside a double-wall cryostat. In fact, this cryostat consists of two independent shells (the “inner” and the “outer” cryostat), and the space in between is evacuated to block convective heat transfer between them. Both shells are made from stainless steel, carefully selected for its low intrinsic radioactive contaminations. The inner cryostat was already closed in Fall 2014, and is kept closed since then in order to keep its inner surface, and the cables and pipes which are already installed inside as clean as possible. It has now been wrapped in superinsulation (the shiny foil on the picture) which is used to block radiative heat transfer. Now, on February 24, 2015, the outer cryostat has been closed for the first time and the insulation vacuum in between is being pumped since then. This is the next step towards filling the first liquid xenon into the XENON1T cryostat.