We bought two "AntiGravityGear Flex Air Ultralight" pillows (at 27gram) some years ago which didn't convince as they lost a little too much air overnight. But the idea of a minimalist valveless pillow substitute appealed in the context of this year's project to get better sleep comfort without significant weight penalty. As a side sleeper, a pillow was high on my list... I tried a few things that failed but eventually thought of foil balloons (the ones designed for helium) which are designed on the same principle as the AntiGravityGear pillows. They do hold air pressure very well but comfort was a problem with the various coverings I tried (buff, pillow cases etc). Then I hit the jackpot with simply inserting the balloon into my quilt or sleeping bag silnylon stuff bag - bingo! To inflate and deflate, I use a tube that came with the AntiGravityGear pillows. Field tested in Italy recently - maintained full air pressure throughout till morning at sub-zero temps. Weight varies between 9 and 10 grams so taking a spare is feasible. But they are surprisingly robust - the weak spot is the tube insertion but if done gently, no signs of wear: my first test balloon is still very much alive in spite of much abuse.