va-Q-shell flex is a customized, flexible insulation system for heat storage tanks consisting of a vacuum insulation panel (VIP) which is covered on one side with a polyester fleece layer, on the other side with a textile layer. It is primarily used as a high-performance insulation layer for heat storage tanks to increase their energy efficiency to a label rating of A and A+ according to the EU regulation 812/2013. Thanks to the polyester fleece, the VIP is protected for example against welding defects and metal shavings. Furthermore the fleece layer prevents unwanted convection. va-Q-shell flex can be delivered in a flat state and can be bent around the tank at the installation site. The system can be used as an additional layer e.g. beneath an ordinary polyester fleece insulation.