For several decades, it seemed that any serious backpack for day hiking or climbing always had a leather bottom. The image of a hiker or climber scrambling over rough terrain, occasionally (or perhaps often) needing to drag their pack over rocks or through brambles, is quite romantic. And when you consider consequences of a catastrophic failure of the bottom of your bag, perhaps miles from the trailhead, it made the extra expense and weight of a heavy leather bottom seem reasonable.
Back when the bags themselves were made of cotton canvas, and there were no heavy-duty synthetic fabrics to offer a better alternative, this made some sense. With the advent of modern synthetic fabrics, however, I find a leather bottom is no longer the best way to make the base of a pack strong and abrasion resistant.
Having spent years repairing almost every type of worn-out and broken backpack you can name, I'll tell you it was very, very rare to see a backpack made of nylon with a truly worn-out bottom. I've seen plenty of poorly constructed bags fail at their bottom seams, but that's due either to inadequate stitching or to the unfinished cut edges of fabric fraying. If anything, a bag would more likely show signs of wearing out from the inside, particularly when it was used to carry climbing hardware or heavy books. Even that was pretty rare.
A leather bottom, in my humble opinion, doesn't add significantly to the durability of a backpack, and in fact, it's a liability in many conditions: the leather can absorb ambient moisture, at the very least wicking it to the inside of the bag, and at its worst, can then freeze in low temperatures.
That visual appeal of a leather bottom, however, is hard to beat. So on The Guide's Pack we offer a tip of the hat to the old leather-bottom style: the exterior of the bottom is coyote brown 1050 denier HT ballistic cloth. But we don't stop there: the bottom is lined with 420d HT Parapack, and the .25" / 6 mm closed-cell foam that pads the back of the bag extends down into the bottom of The Guide's Pack as well, sandwiched between the two layers of fabric. Of course, we double stitch the bottom seams and bar tack the heck out of stress areas, then cover all the cut fabric edges with binding tape. So, even if you're carrying a climbing rack or other sharp, pointy stuff, you needn't worry about the bottom of The Guide's Pack wearing out. Ever.