Make sure that it is waterproof, breathable, and insulated. It is difficult to toprope 5.4s at The Feathers with a frozen rope.
The length of sling should be proportional to the bag size and overall rope mass. For example, a 50 meter 9.2 rope can have a shorter sling since you need to open less of the bag to get it out, than say a 70 meter 10.5 rope.
The bag should provide a harmoneous addition to your fashionable attire for the day. Try to choose a bag that compliments your Prana Top and Capri Pants that you wore that day. In addition, consider the location you are climbing at. Brown is highly dicouraged at Smith Rock and Vantage, since you won't be able to distinguish it from the ground.
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