Publisher Summary This chapter presents heat flow measurements performed on several configurations of vertical prototype lambdaplates feedthroughs. To power the Large Hadron Collider (LHC) superconducting magnets, thousands of busbars will be routed from electrical feedboxes containing saturated helium at 4.5 K to magnets operating in pressurized superfluid helium at 1.9 K. Between those two volumes, the busbars will pass through special feedthroughs also called lambda plates. The measurements show that the electrical insulation around the busbar is very effective in reducing the heat flow between the superfluid helium and the normal helium volumes in vertical lambda plates. These results, confirmed on a multi-busbars lambda plate, demonstrate that it is possible to optimize the thermal properties of a lambda plate by improving the thermal insulation of the busbars on the He I side, without increasing the length of the lambda plate itself.