a partial vacuum of only helium, tightly sealed to keep in the helium. The tight seals will work to make sure that when there is leakage, only helium leaks in. and if there is no helium component to the air outside, you'll just get helium leaking out thus improving your vacuum.
Perhaps there is a hapy medium between air resistance and cushioning? Reducing the air by an amount might help.
Although, I'd be surprised if they hadn't thought of this already :)