Do you where a Camelbak or other hydration pack? YES
If so, how big/how much water does it hold? 100oz
Do you find that your back gets hot under the pack? YES
Would you like a way to let air to go under the pack? YES
Would you pay $15 for something like this? Not separately, but as an "added value" item on a new hydration pack, it would be a nice feature. As was mentioned above, the newer designs of camelbak already have this.