The Hydropack's compact design attaches to the back panel of any hard plastic chest protector, yet it has a 50-ounce bladder and additional compartments and attachment points to carry more essentials. Adding a pack and 50 ounces of water to the back of your chest protector should make it sag relentlessly to the rear and pull the front up. Fly anticipated that, and additional side straps run from the low end of the rear of the pack, under your arms and up to the upper chest of your protector's front plate. These straps settle the entire setup easily in place. I found the Hydropack to be much more comfortable than wearing a separate drink system either under or over a protector. The combination seems less bulky as well, and that is especially important during cold rides. I find it vital to use the front opening of a jacket or vest to control body temperature, so I prefer that outerwear be worn over the protector/water system. I lean toward very light, stuffable jackets, but even the compact ones take a little effort to fit inside this pack. But I'll take the trade-off to have a slimmer overall profile to the pack.At $59.95 the Hydropack is a favorite, a good value, and I have never had to adjust the four main mounting straps. The side straps are designed to be quick-adjusted with just a pull on the loose end each time. The pack is set up to allow the bladder hose to exit on either side.