Waterproof pack liner for gear

Yes. A heavy-duty trash compactor bag makes an excellent pack liner, and for normal backpacking it’s arguably the best value. Current comparisons consistently favor compactor bags or Nylofume liners for keeping the contents of a backpack dry.www.parse.gl

My picks

Nylofume Pack Liner

$6.50

Gossamer Gear Clear Waterproof Pack Liners

$7.50

Six Moon Designs Pack Liner

$25.00

Osprey Ultralight Pack Liner

$47.50

🥇 Best overall: Nylofume Pack Liner
At only 0.9 oz / 25 g, the Nylofume is fully waterproof, 21 × 37 inches, and designed specifically for backpacking. ULA says it's slightly thicker and more durable than an ordinary trash bag.www.ula-equipment.com

💰 Best value: 18-gallon heavy-duty compactor bag
I'd happily use one. Look for a thick, unscented compactor bag, rather than a normal kitchen garbage bag. It's inexpensive, very light, and large enough for most 40–70L packs.

♻️ Best reusable: Six Moon Designs Pack Liner
If you don't want to periodically replace a plastic liner, this is a nice middle ground: waterproof material, taped seams, and a roll-top closure.Six Moon Designs Pack Liner

🏕️ Best premium/reusable: Osprey Ultralight Pack Liner
It's shaped to fit a backpack and has a proper waterproof construction, but you're paying considerably more for convenience and reusability.Osprey Ultralight Pack Liner

How I'd use the compactor bag

1. Put it inside your empty backpack.
2. Put your sleeping bag/quilt, clothes, puffy, electronics, etc. inside.
3. Don't put sharp objects directly against the plastic.
4. Squeeze out excess air.
5. Twist the top, fold/roll it over several times, and tuck it down rather than tying a tight knot.

One important point: a pack liner is for rain, not immersion. If you're doing packrafting, river crossings where the pack could go underwater, or similar activities, I'd put the sleeping bag and other irreplaceable dry gear in actual roll-top dry bags as well.

My personal choice: for ordinary hiking, I'd buy a Nylofume if minimizing weight matters; otherwise, an 18-gallon compactor bag is almost impossible to beat for the money.

If you tell me your pack capacity (e.g. 40L, 55L, 65L), I can tell you which size/type I'd buy and how I'd arrange the liner inside it.