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## Duffel bags - correct sizing?

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### Duffel bags - correct sizing?

My TNF Base Camp 90 liter duffel bag has served me well, but most of the time I wished I had a slightly bigger and lighter duffel bag (with similar features). The Patagonia Black Hole 120 liter duffel looked like a good choice - lighter, similar features, and 30 liters of extra space. I really need that 30 liter space. I wish I could compare the bags side by side, but unfortunately that's not possible as there is no shop in my area that sells the Patagonia's duffel. I did my homework online, and came up with a weird conclusion that the two bags must actually have pretty similar volumes, and no way 30 liter difference!

Here is the math (in meter scale):

TNF Base Camp 90 l:

According to the manufacturer, the bag measures 71x41x41 cm. The volume (in liters) of such a square box (rectangular prism) is ca 119 liters. The TNF duffel is almost a perfect cylinder, so it's volume is then easy to calculate: 71 x (41/2)^2 x Pi = 93.7 liters according to the manufacturer's measurements. It makes sense, no problems here. I did check the measurements at home, and they seem to be correct.

Patagonia Black Hole 120 l:

According to the manufacturer, the bag measures 79x38x36 cm (approximately, after converting inches to cm and rounding up). The volume of such a rectangular prism is ca 108 liters. As the bag is not a rectangular prism, the true volume should always be less than 108 liters. Here I'm assuming that the manufacturer has given measurements for maximum length, width and height (otherwise, what sense do they make?!).

The conclusion is that the two duffel bags must have more or less similar volume, and not differ by 30 liters! Unless Patagonia's official published measurements are something else than I assumed them to be.

So, is the actual volume of the Patagonia Black Hole really 120 liters (any users out there?)? Really 30 liters more than the TNF Base Camp 90l?

JanVanGenk

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### Re: Duffel bags - correct sizing?

I have friends with both the TNF and Patagonia bags you mentioned. They seemed to me to be of a comparable size. If you are looking for larger and lighter bags there are a couple of great options that I really like.

One thing to bear in mind, if you are planning on flying many airlines limit you to 62" in total dimension (length + width + height) without incurring oversize baggage fees which are pretty steep.

I have an Eagle Creek duffel which is light, tough, and cheap. It is 13 years old and has been on many, many road trips and airline flights, strapped to sleds, thrown into and out of bush planes, and is still in great shape. It is about 98 liters (6,000 cubic inches). They make bigger ones too http://www.rei.com/product/848204/eagle ... el-x-large

If you are not concerned about airline size restrictions, look at the Fish Behemoth bag. It is about 160 liters (10,000 cubic inches). I have one and many friends have them as their expedition bags. You could seriously stuff a large person in one. I fit in mine, easily. The bag is made from white haul bag vinyl, so it is super tough but not super heavy. http://www.fishproducts.com/catalog/luggage.html

ExcitableBoy

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JanVanGenk

### Re: Duffel bags - correct sizing?

yes, Airline policies regarding luggage are evolving rapidly. There are also some places where you are limited in size/weight, no matter how much you are willing to spend.

Two months ago, I shipped my first bag. I'd read on the travel sites, this is increasingly the way to go. I'd booked my flight as two round trips, rather than a through flight and had saved \$1100. The baggage fee of \$200.00 per additional bag would've been a downer. You will need to spend some hours working all of this out and come up with a comprehensive plan.

John Duffield

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### Re: Duffel bags - correct sizing?

That was what I was afraid of. If the bags in reality only differ by 10 liter or so, then side by side they must indeed look very comparable in volume. But 30 liter difference should be visible! Anyway, I find it strange that there's such a discrepancy between the advertized measurements and volume.

And indeed, it is used a lot for air travel. I was just hoping to get rid of the bulky but relatively lightweight items (like a down jacket, sleeping bag) in my "hand luggage".

JanVanGenk

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### Re: Duffel bags - correct sizing?

I like the Black hole. Its lighter and kinda easier to access the contents than a TNF. The TNF may win in the long term durability contest but no problems to date with Patagucci. One more thing, this duffle is black but I really recommend if you ever travel to get the most garish colour possible, Makes finding your bag at the airport etc so much easier.

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### Re: Duffel bags - correct sizing?

A cylinder is a more efficient use of space than a rectangular prism, and as the bag is stuffed to that shape the volume will increase.

Exercise: You've given the dimensions of the bag as 79x38x36 cm, aka 108 L.
Area of one side: 38*36 = 1368 cm^2.
Bounds of that side: 38*2+36*2 = 148 cm. If that amount of fabric is deformed to a circle of circumference 148cm, calculate the resulting area.

Hint: it should be around 1743 cm^2, much greater than its rectangular form. (Of course, the bag can't deform to a perfect cylinder if it's not cut that way, but there's also further deformation as the cylinder tries to become a spheroid.) For soft containers, calculating volume is more effectively done via ping pong balls or similar space-filling material (rice? beans?), assuming you have such around.

req

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### Re: Duffel bags - correct sizing?

req,

The calculations concerning your exercise are correct, but I'm still missing something here. If the things are so, then the measurements provided by the manufacturer do not make sense as being maximum length, width and height (especially concerning the width and height).

If you make a circle of that rectangle of 38x36 cm so that the circumference of the both objets is the same, then you end up with the circle whose diameter is 47 cm (after rounding off). Then, the reported maximum measurements for the side panels of such a bag (cylindrical duffel bag) would have to be 47x47 cm, and not 38x36 cm. The assumption of maximum measurements always implies that whatever the shape of the bag, it should always fit inside the square box with the given maximum measurements, and therefore its volume should always be less than or equal to that of the square box. Think, for instance, of the metal frames used to check hand luggage at the airports.

radson (or any other owner of the Pata's Black Hole 120l),

Would you mind providing the measurements of the bag, please?

The photos of the Black Hole suggest that the top side panels are symmetrical trapezoids (corners rounded off, of course). In that case, it would be also nice to get the measurements of that trapezoid (the lower and upper parallel sides, and the height).

JanVanGenk

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### Re: Duffel bags - correct sizing?

Mate, its just a bloody duffle bag. Its not the Hadron Collider.

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Damien Gildea

### Re: Duffel bags - correct sizing?

Consider me crazy if you like. But how can I be sure that the Black Hole is effectively about 30 liters bigger than the Base Camp? That was my question. If not, it makes no sense to me to buy the Black Hole. I have no way to actually see the Black Hole bag. I don't want to buy a pig in a poke. It is volume that matters in this case. If shipping and returns were free of charge, I'd order it. Problem solved. That is unfortunately not the case here.

JanVanGenk

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### Re: Duffel bags - correct sizing?

I see where you're coming from, but the difference in volume between a cube and a sphere is very pronounced. A cubic cloth bag cut to exactly fit a "metal luggage frame" will gain volume once removed from the metal frame and the sides are allowed to bulge outward. Such is the nature of soft-sided duffles; think of Figure C below as a cross-sectional view.

If you shrink the bag so that even fully-bulged it fits within the fame (as in Figure A), the resulting volume of the bag is only about 55% of the the space available in the frame (for comparison, displayed as the smaller gray square).

I think that if a soft-sided bag is cut in a rectangular shape, it makes sense to consider the rectangular dimensions as the "maximum measurements", but they should not be used to calculate volume as the differences can be so large. If you must confine the bag to a rectangular frame, of course, you will necessarily lose significant volume compared to its capacity outside the frame.

(Note: Figure B shows a square and circle with identical areas, all squares were sized at 100px, and diagrams are in 2D rather than 3D. The circle in Figure A thus has an area 79% of the outer square; it would only be 52% of the volume if working in 3D.)

req

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### Re: Duffel bags - correct sizing?

JanVanGenk wrote: I have no way to actually see the Black Hole bag.

Although it is a rare case the manufacturer naming the product appropriately, I think you're gonna find that a greater problem than the volume.
WillP

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### Re: Duffel bags - correct sizing?

Very appropriate name indeed:)

Thanks for your input, req. I indeed assumed (for the sake of simplicity) a situation as in Figure A. That is, take a fully-bulged "perfect" cylindrical duffel and put it inside a rectangular box. In other words, assume that the bag is a true cylinder (rigid, not soft). This approximation works for the Base Camp bag pretty well, because of its true shape (well, I ended up with the right number). The simplified Base Camp calculations fit in the picture: 93.7 l is 79% of 119 l. (Note: as far as volume is concerned, 52% is correct for a cube and a sphere, 79% still holds for a rectangular prism and a cylinder)

Things were not so evident with the Black Hole. When I first saw the measurements, an immediate question arouse: how can a bag that measures 79x38x36 (you instantly think of a box, right?) be that much larger than a bag that measures 71x41x41. That's why I resorted to these calculations in the first place. So I thought that the simplified "rigid-shape" approximation would confirm the Black Hole's volume (as it did for the Base Camp). It apparently didn't. Things went wrong already at the very first step - the volume of the box, 108 l. My assumption implied that one should be able to fit the rigid counterpart of the Black Hole(which likely is a trapezoidal prism) into that box, and thus get an approximation of the bag's volume. Worked pretty well for the Base Camp, but not for the Black Hole.

I'm not sure anymore what those 79x38x36 cm represent. And maybe the Black Hole's sewing pattern is not so straightforward than that of the Base Camp for such an approximation to work properly.

ExcitableBoy said that the two bags seemed to be of a comparable size. Confirmed to a certain degree by my "rigid-box modeling". Not very steep arguments, but still. I compared visually the 90 l Base Camp and a 60 l Ortlieb bag (pretty much the same shape). Could clearly see the difference in volume. I also had a 35 liter Ortlieb bag for comparison.

JanVanGenk

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### Re: Duffel bags - correct sizing?

JanVanGenk,
Your comparison analysis is interesting. Thanks for posting.
FWIW, while absolute volume is somewhat important when comparing dbags, what you are actually putting in the duffle bag may count more than the dbag's absolute volume in terms of efficient load carrying. That is, if you are always and exclusively carrying the same load of pinto beans or ping pong balls (one industry method for calculating dbag volume), then absolute volume may be critical. However, as we know, clunkly alpine gear doesn't always make for the most efficient packing (even if you are stuffing the "open areas" in the dbag with clothes or other collapsibles.

Both the TNF duffle and Patagonia Black Hole Bag are great duffles (but you already knew that ).

More FWIW, at the bottom of this Summitpost review is a list of duffle bag manufacturers (including several European manufacturers). The list may be helpful if you are looking at alternative brands, comparison shopping or wish to identify dbags that might be carried at a local shop (that you can examine first hand).
http://www.summitpost.org/outdoor-gear/ ... e-bag/8474

Be well,
JM

Jesus Malverde

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### Re: Duffel bags - correct sizing?

Just get the XL version of the TNF Base camp and be done with it! The 90L size you currently have is not the biggest one they make. I know, I have two of the 90L (which are the L size) and one of the XL size, which according to REI are 155 liters in size.
I recently measured the XL size to determine the total of length, width, and height and it was compliant with the airline maximum for international travel. Although I ended up deciding to take 2 of the L size to Peru, other climbers took XL size Base camp duffels and had no issues, including folks who travelled from Europe.

Norris

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### Re: Duffel bags - correct sizing?

I hav a Patagonia Black Hole in the largest size and a large TNF duffel. The one thing I really like is taht while the Patagonia Blak Hole is really bomber construction and takes a lot of abuse,its also REALLY light compared to any other bag in its size and quality. Given airline flight regulations on baggage weight, I am really picky about how heavy my bag is. Some bags in that size weigh upto 14lbs which means only 36 lbs of gear goes into it or 28% of my luggage weight is just the weight of the luggage....

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