I tested my two backpacks of very different sizes, one day pack and one larger backpacking pack. As expected, they became heavier when wet, but the results were a bit surprising. Keep reading.
What I Have Done
In short, I used my two backpacks, one for multi-day tours and one day pack, to check how much heavier they become when wet.
Those were my Osprey Stratos 24 (the first picture below), and Deuter Futura Vario 50+10 shown in the second picture. The latter is formally discontinued at Deuter, but they have launched the Deuter Futura Air Trek 50+10 which is practically the same pack, just to know if you want to order it.
The reasons for using such different packs are as follows.
First, they are for different loads so the hip belts are with very different padding, and this should also imply different padding on the shoulder harness.
The larger pack is also with a huge lumbar padding, and this is absent in the smaller pack because of its completely different design with a continuous tensioned mesh. I expected that the larger Deuter pack would become much heavier when wet.
Second, I wanted to make the testing and results useful for more people that use different packs, just to give them some idea of what they can expect.
More precisely, if they have results for such different packs, then any of their packs with the volume in between these two should give results that are in between the results obtained in my testing, more or less.
I simply measured the weight of the packs when they were dry, and then put them under shower to become wet, and then checked the weight again.
Curious About Wet Backpack Weight? Here’s What I Have Found
It turned out that both backpacks gained half a kilogram of weight when they became wet. In other words, each of them absorbed half a liter of water.
For the lighter day pack this implied that it became 40% heavier when wet. The larger pack became 24% heavier.
These numbers are far from negligible.
The mentioned Osprey Stratos 24 pack normally weighs 2.756 lb (1.25 kg). As you see, it is not light for its size.
But, as described above, its weight became 3.86 lb (1.75 kg) when it was wet. So the weight of the wet day pack was in the range of some large backpacking packs like the Big Agnes Parkview 63L Pack for Men.
I expected that the Deuter Futura pack would absorb more water and become much heavier. Surprisingly, the increased weight was the same in both.
The Deuter pack weight is normally 4.56 lb (2.07 kg), so it is moderately heavy. But when wet, it measured 5.66 lb (2.57 kg), and this puts it in the group of heavy backpacks.
The fabric is nylon in both, therefore the total water absorbance is expected to be similar. On the other hand, these are backpacks that I have been using for a number of years already. So whatever water repellents they have had when they came from the factory, it was surely washed out and vanished from their fabric.
So it seems that the padding in that particular Osprey’s pack is simply more hydrophilic and it absorbed the same amount of water although the pack is smaller and with far less padding than the Deuter’s pack.
Please see more about my testing in this video:
Pack Cover Weight vs Wet Pack Weight
So there is no doubt, a wet pack may becomes considerably heavier compared to its weight when it is dry.
Now, how to prevent it from becoming wet? One way would be to use a rain cover. Most of my backpacks come with a rain cover. I am a mountaineer and this is in the area where having such a cover is essential.
With a rain cover, the main body of the pack is protected from the rain. This includes the gear in the main compartment and in the pockets of the pack, plus the fabric of the pack itself.
But a rain cover itself adds weight. How much weight exactly? Well, I just checked with the Osprey Stratos 24 pack because it comes with a rain cover in a dedicated pocket on the bottom. The weight of the rain cover is 71 grams (2.5 ounces).
Now, speaking completely generally, if your pack has no rain cover, would it make sense to buy one, so that the pack does not become heavier when wet?
My answer is: probably yes; the half kilogram of extra weight in my experiment is partly due to water absorbed by the pack’s main body, and most likely this is more than the rain cover weight.
But, as mentioned above, a rain cover would protect only the main body of the pack. The harness and hip belt with their padding, that absorbs water like a sponge, would remain unprotected.
However, as I mentioned, I want to have a rain cover to protect the gear from becoming wet, and the dry/wet pack weight difference is of a secondary importance for me. In any case, having a rain cover for a pack is a bonus.
How About Using a Plastic Bag Instead of a Backpack Rain Cover?
I know, some people claim that a simple plastic bag is good enough. Place it in the pack and then put your stuff in it.
But how about pack’s pockets and the gear inside? Would you have separate smaller plastic bags for each of them?
How about the pack’s body fabric? It will not be protected so it will get wet and heavy.
By the way, such plastic bags are not weightless. Yes, this is just about grams, but the whole story here is about avoiding extra grams.
All in all, in my view, plastic bags instead of a rain cover are not a great option.
What Is the Solution?
I do not think there is any perfect option, and if you do not wish to get wet, do not go outdoors. Using a rain cover will not completely help because the harness and the hip belt are not covered and protected.
If you want to avoid the discussed extra weight with your heavy and wet pack, perhaps it is best to use a poncho that covers the pack too. Though not just any rain poncho; some are designed to cover both the backpack and your body, so this is the type you will need.
The picture below shows one extraordinary versatile and functional example, the Sea to Summit Nylon Tarp Poncho 4-in-1 Raincoat:
Though, a poncho also adds weight, the example from the Sea to Summit weighs 400 grams (14 ounces). But you have seen 4-in-1 in the name. This is a raincoat, a pack cover, a groundsheet, and a tarp, all in one item. You can read more about it on their site, note also that they have more models to offer.
In the picture below, you can see what I carry in the pack, my own poncho weighs 278 grams (9.8 ounces). As you realize, it is not particularly light, but I think it is worth having it in the pack, unless it is extremely windy.
I had such a bad experience last summer on my hiking tour to Lake Sorapis in the Dolomites. I was completely wet although I had all the usual waterproof layers.
Final Thoughts
In conclusion, the experiment of testing wet backpack weight yielded notable results, revealing that both the Osprey Stratos 24 day pack and the Deuter Futura Vario 50+10 backpack gained half a kilogram in weight when soaked, equivalent to absorbing half a liter of water.
Surprisingly, despite their distinct designs and sizes, both packs exhibited a similar increase in weight, with the day pack becoming 40% heavier when wet, and the larger pack 24% heavier.
From my own experience in almost 40 years of mountaineering, a rain cover offers a good protection to the main body of the pack. But it does not prevent the absorption of water by the harness and hip belt, highlighting the challenge of maintaining a lightweight pack in wet conditions.
Furthermore, alternatives such as using plastic bags instead of a rain cover are impractical, as they fail to fully protect the pack’s contents and body of the pack, and they add weight themselves.
Considering the limitations of rain covers and plastic bags, employing a poncho that covers both the backpack and the body could be a potential solution to mitigate the added weight of a wet pack, albeit with its own weight considerations.
Thank you for reading. Bookmark this site and come again, this will keep you informed because I add texts here regularly.
Let me know if you have questions or comments, there is a comment box below. Have a nice day.
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