PowPow- Both boots are rated to -40°. The Caribus weigh slightly more than the Pacs. The Caribu also has a deeper tread on its sole, making it slightly better for off-road hikes and icy areas. . The tread on the Pacs doesn't grip as well. The Caribus' upper is a nubuck leather while these are embossed leather. I believe nubuck leather is tougher. Here is the difference between the two liners: "ThermoPlus® InnerBoots: Pioneered by Sorel in 1993 after extensive field testing. ThermoPlus® InnerBoots provide superb warmth, moisture transfer, comfort, and durability. An advanced four-layer construction wicks perspiration from the foot, maximizes thermal insulation, and reflects body heat back to the foot for a warm, dry foot "climate". 1. Soft, short loop polyester Minktex® (green inner layer) maximizes contact to quickly wick perspiration from the foot. 2. Black polypropylene core insulates and facilitates wicking process. 3. Radiantex® foil reflects body heat back to the foot. 4. Polyester/viscose blend (camel outerlayer) insulates and stores moisture away from the foot. Washable/Recycled InnerBoots: Pre-consumer recycled polyester. Ideal for children's boots where InnerBoots are exposed to excessive dirt and perspiration. A unique two-layer construction wicks moisture from feet and provides excellent insulation."