MYOG No. 5 – Cuben Fiber Roll Top Dry Bag

GEAR: Cuben Fiber Roll Top Dry Bag

WEIGHT: 0.7 ounces

DIMENSIONS: 10″ x 24″ pseudo envelope

COST TO MAKE: ~$15

BEST USE: Sleeping bag waterproof stuff sack

WILL I USE IT?: I use it all the time

Bottom
Bottom

Want the most ultralight gear possible? Yes please. Shave a few grams by switching out the silnylon compression sack for a waterproof roll top cuben fiber dry bag? Why not? Keep my bag extra dry with another layer of waterproofing? Sure! I made a few pieces of gear in preparation for the rainy thru-hike that is the VT Long Trail and this is one of them.

IMG_8517
Bag with roll top closure

The dry bag is made using 1.0 oz/sqyd cuben fiber, single sided cuben fiber tape (waterproofing), and one 1/2″ side release buckle. I sewed the fabric into a tube shape, sewed the middle of the bottom together, then sewed and cut the corners to create a bottom to the bag so that it has more shape than an envelope. I added reinforcement stitching so the bag can withstand the pressure of my sleeping bag trying to burst it open, and added single sided cuben tape for extra waterproofing/seam taping. The roll top closure holds shape by folding the top edge over and with an extra piece of folded over cuben fiber. The buckle is attached and sewn to the bag top.

Side reinforcement stitching
Side reinforcement stitching

Does it work? Yes! It fits my feathered friends egret 20 down bag perfectly. I’ve used it over 50 days of compression and going strong.

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First ultralight gear made: dry bag!

Ultralight cuben fiber dry sack!
Ultralight cuben fiber dry sack weighing in at a teeny weeny 10 grams

Gear: 8-Liter 0.33 oz/sqyd Cuben Fiber Roll-Top Dry Sack.

Weight: 10 grams.

Dimensions: 10″ x 20″

Cost to make: $10. Comparable retail cost: $20-$30. Savings: about $10-$20 (100-200%)

Use: Dry bag for quilt, clothes, or small sleeping bag.

Will I use it?: Yes, as soon as I make myself a quilt! Right now my sleeping bag is too big to fit inside…

Taped seams
Taped seams

In case you haven’t figured it out yet, this post is about gear making (Aka MYOG, or Make Your Own Gear). I confess – I haven’t been in the mountains much lately. Instead of hitting the hills, I’ve been climbing indoors at Vertical World, running (including a hilly 5k in Interlaken Park), and making gear for my next adventure! Yes, I’ve officially caught the ultralight bug.

This is my first piece of ultralight gear – a Cuben fiber roll-top dry sack with the lightest possible cuben fiber out there (at 0.33 oz/sqyd).

So what is cuben fiber? It’s an amazing super light fabric used in ultralight gear making, among other things. “Cuben Fiber is a high-performance, non-woven, rip-stop, composite laminate developed in the 1990s by a nuclear weapons physicist and an aerospace composite engineer.  Originally designed for use in world-class sailing, it is ideal for certain applications in lightweight and ultralight outdoor gear due to its unmatched strength-to-weight ratio”, according to lightweight gear makers at Hyperlight Mountain Gear. “Technically speaking, Cuben fiber is a laminated fabric made using patented technologies with unidirectional prepregnated tapes of in-line plasma treated fibers that are spread into mono-filament level films.  In more simple terms, Cuben fiber is made by sandwiching Spectra or Dyneema polyethylene fiber filaments a thousandth of an inch thick, in various arrangements between thin outer layers of polyester film.  The “sandwich” is then melded together in a high-pressure autoclave. Cuben fiber is lightweight, highly durable, and is 50-70% lighter than Kevlar, four times stronger than Kevlar, and allows flex without losing strength.  It is also less than half the weight of silnylon, has low specific gravity (floats on water), high chemical resistance, excellent UV resistance and is 100% waterproof.”

Square sewn and taped bottom construction
Square sewn and taped bottom construction

In short – ultralight, ultra strong, and waterproof. Perfect for tents, tarps, dry bags, stuff sacks, etc. It comes in weights ranging from 0.33 oz/sqyd-1.43 oz/sqyd plus as a hybrid with other materials.

This dry bag is constructed with the lightest possible cuben – 0.33 oz/sqyd. Most of the seams are taped with double sided cuben tape. I folded the bottom and sewed the corners in order to get a box like shape, then taped the outside with single sided cuben tape for waterproofing. The top edge is reinforced with more 0.33 oz/sqyd cuben rolled/folded over, then taped with single sided cuben tape on which a buckle is attached for closure.

It works well and will hold a small quilt. Because it is so likely to puncture, I consider it highly water resistant as opposed to fully waterproof. In fact, upon testing (filling with water!), there were a few teeny tiny holes through which water seeped over time. It should function well inside a pack in rainy conditions, but probably not fully submerged in a river (which I don’t intend to do).

So overall – first ultralight gear making was a success! Next on the horizon: tiny bug mesh tent, tyvek ground cloth with toe splash guard, 2 person tarp, and tarp/poncho…

Success
Success