Measurement parameters and exact numbers can be found in the Table . Nevertheless, it is worth mentioning that our membranes offer a performance much higher than comparable materials and surpasses the Robeson upper bound 2008, which is also only comparing data for 1:1 mixture of He and CH 4 . With the MIL-116(Ga-formate) MMMs with 20 wt.% we can upgrade He from 4 % to a purity of 99.997% (technical grade of He 4.6) directly from a natural gas stream in a one-step process.