Rain covers or liners?

Liners vs. covers — there will never be "one right answer".

I think first and foremost — you have to look at how YOU pack — and how much you might be willing to adapt (if at all). Are you comfy with dropping most everything into one big hole? Then a liner makes sense. OTOH, if you are into organizing — i.e. separate sleeping bag compartment, multiple outside pockets, bungee cords, daisy chains, etc. — then you'll likely be happier with a cover.

Secondarily, you should consider the design and fabric of the pack itself. Pack covers will never provide 100% protection — only a liner twisted shut can do that. OTOH, if your pack is made with beefy and old-fashioned pack cloth that absorbs a ton of water, then maybe a cover is the way to go.

If fording streams, definitely a liner. A liner twisted shut with the end pointing downward and with the pack closed and cinched tight will be rainproof. But if canoeing or fording streams, you may want to rubber band the end tight for added waterproofness.

Now, focusing on liners… silnylon liners vs. good ol' garbage bags? I would go for the 2mm contractor bags (note the comparison that many so-called heavy duty yard bags come in 0.9mm or less than half of contractor bags). IMO, with just a bit of common sense care — contractor bags are very tear and abrasion resistant. Any object sharp enough to puncture the bag will be sharp enough to damage your backpack too (hence common sense care). Silnylon may be a tad lighter for the same tear strength, but they are just as weak in the puncture department.

It depends a lot on your hiking terrain and climate. I often have to ford rivers, and wouldn't trust my gear to just a pack cover. Also, most pack covers (at least the lighter ones) aren't tough enough to stand up to off trail abuse. And pack covers are really unacceptable if you need to access the contents of your pack during a deluge. So I go with a totally bombproof liner for my 'must stay dry' gear, and put everything else on top of that. YMMV.

Both, I have a Zpacks 1.2 oz pack cover and for my down insulation material (sleeping bag and jacket) the Granite Gear Dryvents Drybloc, total weight is 2.9 oz for both combined.

i agree with lynn, i have the granite gear drysack you refered to for my down bag. that way everything else is still accessable. i have not had to test the drysack luckily, but the quality is very good.

Both here as well. Double safety.

I prefer liners. Covers keep me from reaching my easy-reach side pockets, and can get caught on brush. Quality liners can also be sealed up with some air trapped inside, making a pack more bouyant for use while paddling.

Pack covers are nice to keep the outside of your pack dry during a shower. However, during prolonged rains the water runs down your back (where the pack cover isn't) and soaks into the pack. Pack covers are also useless in case of immersion. I know I'm not the only hiker around who has fallen while fording a stream! I have regularly used a pack cover only because my pack is part of my pillow so it's nice to have the outside surface dry.

For quite a few years I've used 2-mil trash compactor bags as pack liners. (Watch out–some brands, especially Walmart's, are perfumed!) They are certainly the least expensive solution.

It appears that lots of folks just rely on stuff sacks. However, they are not waterproof (take one into the shower, and you'll quickly see that the closure lets lots of water in). You can supplement stuff sacks with mylar turkey roasting bags (from the supermarket). Some just use the mylar bags. However, if you squish the roasting bag too hard, the seam may explode. And the combination of stuff sack plus mylar bag is as heavy as a lightweight dry bag.

Last spring I got tired of shoving small items down into the trash compactor bag only to have them pop right back out again thanks to the slippery surface. I went to REI looking for dry bags, but most of them are at least twice as heavy as a stuff sack. However, I did buy a small Sea-to-Summit Ultra-Sil dry bag for my first aid/essentials kit. These bags have had a bad rep in the past because they have leaked water through the fabric. However, this bag and the subsequent ones I bought passed the "turn inside out and fill with tap water in the bathtub" test–no leakage at all. (Obviously S-to-S has made considerable improvements in its product!) I therefore bought two more Sea-to-Summit Ultra Sil Dry Bags–one for my sleeping bag and sleeping clothes and the second (smaller) for my insulating outerwear. I carefully tested both bags in the bathtub before using them to be sure, and they definitely do keep the water out. These dry bags are no heavier than a silnylon stuff sack plus turkey bag, and the extra weight over the weight of a stuff sack for the two Sea-to-Summit bags is about the weight of the trash compactor bag.

These dry bags were inadvertently well-tested during my above mentioned dip in the stream last summer, and everything inside stayed dry. Since it was raining (it rained constantly for four days on that trip) and I was 2 days' hike from the trailhead, I was very glad that the dry bags worked!

So I've ditched the trash compactor bag/pack liner and use the dry bags for my critical gear (sleeping bag and clothing). I may also ditch the pack cover–I will try this out during short trips this spring. I too have been eyeing the Z-Packs cuben fiber pack cover as it is several ounces lighter than my current Integral Designs pack cover.

Poncho over me and my pack. No water down the back of the pack this way.
Waterproof pack material (XPac from Dim Poly)
Silnylon stuff sacks
PE plastic bags inside important stuff sacks (you can buy them in bulk, or pinch them from the fruit shop, or use freezer bags).

Two months wet weather in France in 2007. All gear stayed dry.

Mind you, for swimming rivers in fine weather, I do use a garbage bag pack liner as well. Paranoia… and dry.

It's not hard.

Cheers

I forgot about ponchos. That would get around the standard pack cover's partial coverage problem…

Ponchos can flap in the winds. And they can get punctured more easily than a liner nicely residing inside your pack.

I use a contractor's bag as a liner and I am completely happy with its performance — having hiked for hours in hard rain and suffered a good river dunking. However, as I alluded to above, it does mean packing a certain way. For me, everything except the stuff I need during the day go inside the liner and stay inside. Stuff that I need reside in my pack's side, front, and hipbelt pockets.

Alas, no solution is perfect… YMMV.