Nylofume® Waterproof Pack Liner - 27g

Haven't used them yet but I'm sure based on your recommendation that they will do the job just fine.

Seem pretty strong for weight.

Lighter and more robust than a garbage bag. Repairable with tape if they puncture on trail. I used two of these (one for camp clothes and sleep system, the other for everything else) for a 1000km hike with no issues. Don't try to over stuff them, better to use two bags. Much lighter than a silnylon pack liner.

You would be mad to not use one of these, weather is hard to predict. They seem to last me at least a year before ill get a small hole, which is usually repairable

These are relatively cheap, lightweight and durable. Stronger than a plastic bag and shaped to suit a hiking backpack, making it easy to use.
A simple and effective way to keep your gear dry inside your pack. Highly recommend!