About 1 month ago I had ordered this pillow and filled immediately after the delivery with 3.5 liters of water and increased after a few days getting used to 4 liters capacity.
If you strained a little, you get the water actually blubberfrei filled, or the air pushed out so that the nightly "bubbling" with little or no notice.
With my old 80/80's pillows I have repeatedly turned the pillow at night, folded and somehow stuffed between the mattress and head. That's not much exciting and relaxing. This cushions the "water trough" moved with the turning of the head on the pillow. The head is thus always fine in a "dump". In addition, the cushion is so heavy that you at night not even be tempted to rotate or turn the 4-5 kg cushion. This, I feel, really relaxed sleep. Whether that is orthopedically sensible or is a medical revolution, I can not answer.
I like the Kiseen, I do not want to miss and have my skeptical wife then after a week also ordered a pillow - she shares mittlwerweile my enthusiasm.
So thumbs up!
