It may be a blend with 1234yf. A lot of those aftermarket kits use refrigerant blends to get "the best of everything" such as lower operating pressures, higher heat saturation capability, etc. Unfortunately with most blends if one gets a leak the whole system must be evacuated (which should be done anyway) and refilled since the different refrigerants may leak at different rates due to molecule size. This means one shouldn't just top it off since it changes the blend.
Another refrigerant that seems to be better than 12, 134a and was actually a competing refrigerant was 152a. Lots of data on youtube since it's the ingredient in those canned air products. It supposedly has performance better than 134a with pressures that are similar to r12 with a GWP (greenhouse warming potential) about 1/10th that of 134a. I did that conversion on my '94 Oldsmobile when I rebuilt the A/C system a couple years ago and noticed it did have similar performance to 134 and didn't seem to impact my mpg quite as much, maybe 1-2 mpg better though I didn't really have long to test as it was after the halfway point of summer. It did use about 1/3 less than 134a called for (30oz to 21oz) and pressures were a good 50-70 psi lower on the high side which I'm sure helped mpg since the compressor didn't have to work as hard.
However all that said, Since most of us know relatively little about the Volts refrigerant system and how foreign refrigerants may impact the 300V compressor, BTM system, etc. perhaps it's just best to stick with what the engineers designed for use, especially since I recall reading they don't even recommend home top offs with small cans due to the inclusion of oil in most of those cans but rather using a 30lb tank.
