Waterproofing a pack

[Wandering Archer]

I'm going to agree with the pack liner. I wouldn't put anything on the pack itself.
Trash compactor bags are cheap, tough, and light. That's what I use for backpacking.
If you expect to be in a heavy downpour and don't want the pack to get heavy with water, then buy a sip nylon pack cover.
They aren't too expensive and will protect the outside of your bag.

Leave the bag fabric alone if you ask me.
In my experience, silicone treatments wear out quickly, and aren't there when you finally need it.
Wax and/or oil treatments are better but add a lot of weight and can add an oily feel and ruin the breathability of the fabric.

[slowbowjoe]

Yup, pack cover is the way to keep the pack itself dry. Often enough to take care of what's inside, too.

I have used Scotchguard with good results. Use the stronger, automotive upholstery type and give it a couple of coats.