Silnylon is one of the lightest technical fabrics that home sewers can buy. It’s often used for shelter systems but I’ve been curious about using it for backpacking packs. Jan Rezac created an ultralight waterproof backpack using silnylon. This post is a how to sew an ultralight silnylon backpack Rezac Pack MK III project review.
The link to Jan Rezac’s project tutorial is:
This project is published under Creative Commons Attribution Noncommercial Share Alike 3.0 Unported License [https://creativecommons.org/licenses/by-nc-sa/3.0/] for non-commercial use.
For the purposes of my review, I’m going to summarize the basic steps, tell you what I did differently (if anything) and share my general thoughts about sewing the project.
The ultralight silnylon backpack is a partial shell designed to used with a waterproof drybag, which eliminates the need for either a pack cover, pack liner or waterproof stuffsacks. The front panel only covers the lower portion of the drybag and your sleeping pad is used as a frame. Jan reports a weight of 320 g (including the drybag) for this project. I estimate that Jan’s pattern makes an ~ 35 L (~2136 cubic inches) capacity pack with the following dimensions: 52 cm tall x 30 cm wide x 22.5 cm deep (20.5” tall x 12” wide x 8.8” deep).
I extended the height of my ultralight pack by one-curved section (see pattern) in order to better accommodate my Thermarest ¾ Length sleeping pad (circa ~ 1999). My finished pack was ~ 65 cm tall x 30 cm wide x 22.5 cm deep (25.6” tall x 12” wide x 8.8” deep) for a capacity of ~44 L (~2685 cubic inches). It weighs ~ 330 g (11.6 oz) excluding the drybag.
Step 0 Gather Materials
You can use uncoated, parachute nylon or silicone coated nylon (aka silnylon) for the main fabric for this project. The scraps of 20D silnylon I had leftover from making my YAMA Mountain Gear Net Tent were large enough for this project. I also used 420D polyurethane coated nylon, bag mesh and some synthetic material (probably acrylic) from rice bags (don’t do this; this fabric didn’t last long enough for me to finish sewing this pack). You’ll also need assorted plastic buckles, webbing, elastic, and eva foam.
Step 1 Hip Belt
I had trouble finding 3 mm thick eva foam so I purchased some 2 mm thick eva foam and used low odour contact cement to glue two layers of it together.
I prefer a textured fabric on the sides of the hip belt and shoulder straps that will be against my clothing so I used 420D nylon for the inner pieces. My foam was a little thicker than the recommended foam, so I did have to trim my hip belt foam a little in order for it to fit inside the hip belt casing. I used my Teflon presser for this project and used my sewing machine’s longest stitch to sew through the foam.
Out of curiosity, I put my finished hip belt on a scale. It weighed ~ 100 g.
Step 2 Shoulder Straps
I used silnylon for the shoulder strap exteriors and 420D polyurethane coated nylon for the interiors.
My shoulder strap foam was sourced from eva foam floor tiles. It was ~ 8mm thick (6mm thick eva foam is recommended). Snipping into (but not through) the seam allowance along the curves and folding the foam in half lengthwise made it easier to ease the foam inside the fabric casings.
I was surprised to discover that my sewing machine could topstitch through the assembled shoulder straps. I had considered using webbing to sew on the ladderlocks but discovered that only grossgrain ribbon was thin enough to fit under the presser foot. Grossgrain ribbon is slippery so I sewed it to my ladderlocks then sewed it to the shoulder straps.
Step 3 Side Panels
Sewing the buckles on can be tricky as you’re working with the side panels when they’re inside out. I used 5 cm (1.9”) long pieces of webbing to attach the buckles and found there wasn’t enough webbing to both extend the webbing ~3 cm (1.2”) past the edge of the fabric and maintain the same seam allowance as the other side panel seams. As a result I used a 6 mm (¼”) seam allowance for both the buckles and webbing straps. I recommend you use longer pieces of webbing and the original seam allowance.
Step 4 Front Panel
The tutorial and accompanying photographs show a notch in the corner of the front panel but don’t describe the dimensions of that notch. I cut mine 6.5 cm wide and 3.5 cm deep (2.6” wide by 1.4” deep). There wasn’t quite enough room for the side hem so I recommend cutting the notch 6.0 cm wide and 3.5 cm deep (2.4” wide and 1.4” deep).
Step 5 Side Pockets
Two options for preparing the stretchy tops of the pockets were given. I made bungee sleeves from strips of 420D nylon 3.5 cm wide and 27 cm long (1.4” wide by 10.6” long). I hemmed each strip 0.6 cm (1/4”) then sewed the un-hemmed long edge to the top of the mesh with a 6mm seam allowance. Next I folded the fabric strip down and sewed it to the mesh. My bodkin made it easy to thread the bungee cord through the channel.
I had some trouble sewing the mesh pockets to the side panels. The inner layer of silnylon wrinkled up when I folded the mesh pockets over to sew the second vertical seam. It was time consuming to rip these stitches. Make sure you pull all the layers taught to avoid having to do so.
Step 6 Back Panel
Marking the centre of the back panel makes it easier to keep everything symmetrical.
Step 7 Final Assembly
Sew the final seams twice for strength thensew some extra stitches over the webbing and along the rear bottom seam. I sewed the side seams with the silnylon as the top layer so that I could use some gentle tension to keep it from wrinkling. This worked great and I didn’t have to rip any stitches.
Sewing the hip belt suspension elastic was difficult as the hip belt kept getting in the way. I sewed the front and bottom seam seams with the side panels on top so that I could see where the bottom corner was and pivot my presser foot accordingly.
My first two attempts to sew the rear bottom seam with the back panel on top resulted in puckered fabric and ripped stitches. It ended in disaster when the acrylic bottom piece tore perpendicular to the seam. Glad I discovered how weak this fabric is at home rather that on the trail. I spent considerable time ripping stitches to replace the bottom panel with one made of 420D nylon.
Sewing the rear bottom seam with the back panel on the bottom worked better for me, but I still had to rip stitches. I ended up hand basting it then finishing it with my sewing machine. The final step is creating the top sleeping pad/foam sheet pocket.
That’s it! Your new ultralight backpack is now ready for use!
Here are some photos of my finished ultralight backpack:
Most of my backpacking gear is in storage but I’ll be adding some more photos of this backpack loaded up with gear in the future.
I estimated some measurements based on the illustrations and my previous experience sewing backpacking packs. I didn’t refer to the additional project photos often, but they are a great resource. The ultralight backpack Rezac pack size and shape is one that provides a functional fit for a variety of body types. Customizing the hip belt and/or shoulder straps wont be necessary for most people.
Generally speaking, diy backpacking gear projects are intermediate sewing projects. The ultralight backpack Rezac pack project is no exception. Technical fabrics (like silnylon), webbing and plastic hardware are not as widely available as cotton fabrics. Silnylon is an especially slippery fabric which makes sewing it challenging. Other challenges include working with curved lines and EVA foam.
One of the aims of this project was to create backpack that was significantly lighter than my 2.5 kg (5.5 pound), 60 L (3600 cubic inch) internal frame pack. My ~44 L (~2685 cubic inches) ultralight backpack Rezac pack weighs ~ 330 g (11.6 oz) making it the lightest backpacking pack I’ve sewn with a capacity over 30L (my 28 L SUL silnylon daypack weighs 155 g). I’m truly amazed that a pack this large could weigh so little. I’ll test this ultralight backpack on the trail and add some photos of it in use.
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