Most of us use some forms of pack liner. There are many on the market with the high end ultralight ones predominantly based around silnylon to keep the weight down. Low end versions are usually PU coated nylon and are somewhat heavier than the sil versions.
All of them have drawbacks. Silnylon is expensive and has really poor abrasion resistance. All of my sea to summit and exped ultralight liners have holed and are no longer waterproof. It's a lot of fuss to patch them and I grew tired of wasting so much money on products that don't last.
PU coated is largely too heavy for consideration. And the coating does tend to separate after abrasion and moisture exposure. Having suffered these issues I started researching ultralight alternatives.
For a good while I used rubble sacks but I found they didn't fit the three dimensional shape of my packs very well.
With this in mind I have now sourced 45 litre 3d clear 50% recycled polyethylene bags from Europe which finally solve all of my issues. They are very light at 30g and are extremely tough for their weight. Ive had feedback from customers who have used these on a two month thru hike in the states with no problems. They have a 12 inch opening 8 inch depth and are 28 inches tall and are designed for packs of up to 45l which should cover most ultralighters needs. They will conform easily.to larger depth packs easily with far less loss of space than a non gusseted bag
They are not dry bags as the top is open but I've never had a problem with water ingress. Simply put moisture sensitive items like sleeping bag and clothes in the bag, add other items and roll the top down or tie off the top as pictured . I then usually whack my cook kit on top of the rolled bag to keep it sealed.
They also tape or tie up really well if you want to store gear in something to keep dust and muck off at home but easily see what's in the bag.
COMPLETELY FOOD SAFE UNLIKE MOST LINERS
PACK OF 10
