I have been using a Camelbak Mule pack for the past few years and recently decided to try another pack with the Osprey Viper.
The Mule can hold 3 liters/100 ounces. I was looking for something smaller and that is where I found the Viper at 80 ounces.
I have had the Mule for almost 3 years and put it through the ringer with sweat and grime and briers. I have never had a tear or any problem with the pack.
The Viper is smaller but in some cases that can be better when you are trying to travel light and move quicker. I found that putting 100 ounces of water on my back for a 100 mile plus off road journey can put extra stress on your body. But if you have to carry it – this is one definite option.
You can load up a fair amount of gear in the Mule as it has a 9 liter / 500 cu inch space. But believe it or not the Viper has 549 cu inches of volume (I am double checking these numbers). Typically I carry a small medical kit, multi tool, emergency lighter, and a full bladder (if it is hot weather and I have a ways to go). Most of the time I go with about 50 to 75 ounces and sometimes I put a jacket in the back pouch.
The fabric on the Camelbak Mule is very durable and mildew resistant. I have had the bag fully wet from sweat, or river water or rain, as long as you half way try to dry it out it does not mildew.
Both bags have a waist strap but I have never used it despite carrying a full load (water, food, med kit). This includes bikepacking down a steep rocky single track – I just dont use the waist strap.
I have not used it but the Viper has a helmet connect system on the back.
If I had a choice right now I would stay with the Viper even though the Mule has been very good to me and I am sure it will continue to have a few more adventures.
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