First post so, err, hello!

Whilst I await my order from extremtextil, I’ve been thinking about seams for my bivi bag.
I’m going for a groundsheet style base with a breathable top and simple drawstring around the head/face.
From google I’ve learnt that a felled type seam might be best for strength and waterproof-ness of the seams. However, I’m struggling to see how I can fell this seam once I’ve done the initial pass without some serious bunching up issues around the sewing machine (as the bag will be sewed inside out, all the way around)
Since I will be using an iron on seam-seal anyway, would a single regular stitch seam cut it?
I’m thinking the seams might well see a bit of stress from getting in and out and general wriggling but hoping the seam seal will provide some backup here.

Any advice greatly appreciated.

I’m a relative beginner at all this, my other MYOG items have been a bothy shelter, some dry bags and an apex quilt, inspired entirely as someone posted on here a while ago.

Thanks.

what material you using? can you flat fell seam (practiced it)? i find it veeeeery difficult tbh...

consider this too:

https://mountainlaureldesigns.com/how-t ... igns-tent/

that stuff is dead easy to use... i also use dots on the floor to stop the inflatable matt moving around.

also, the double sided tape for dcf with a thin dcf layer is waterproofing and can be stuck to some non dcf material....might be easier than iron on?

tbh, a bivi sack is often so wet from condensation, a simple folded corner bathtub design, with a normal seam might well cut it without any seam seal....

I just used normal seams on mine and it's been fine. The flat felled seam done in two passes is probably no stronger than a normal seam due to the way it's sewn. I assume that there is a special machine that does the folding and sews two rows of stitches all at once that the commercial text manufacturers use.

I also used a non-breathable base and breathable top and it works well. You could sew some reinforcing patches over the seam at the opening as that will be the main stress point when getting in and out.

Thank you both for the replies, I felled my first seam yesterday while repairing a pair of shorts that had a few, how shall I say - stressed - seams... Not sure I'd want to repeat the process on a whole bivvy bag!

Sounds like a normal seam will cut it and then sealed somehow. Dots of sealant on the floor to keep the mat in place sounds like a great tip!

Thanks.

How did this work out?
I’m considering making a Bivi bag

It’s been absolutely fine with a single straight stitch and then an iron on seam seal strip.
I made it with a groundsheet type base and a 2.5layer breathable top layer, traced the shape from a bag I had already and then adjusted so it would fit my length of material (military bivi bags are huge!) It’s 2D to keep it simple. I took inspiration for the drawcord from the Alpkit bags shown online. I cut a hole in the top layer for access and egress, edged this with 50mm grosgrain folded over to make a cord channel.
I think marking out and cutting took the most time followed by seam sealing, the stitching itself is quite quick.
Used it a fair bit last summer/autumn. The breathability of the top layer isn’t amazing but it’s not soaked in there either. Plenty of room for me, I don’t find my mat slides around too much. Total weight 350g.

jBay wrote: ↑Fri Feb 19, 2021 11:06 pm How did this work out?
I’m considering making a Bivi bag

I made a bivvy bag (25 years) ago but it was a medium weight 1 ply goretex. Lighter than a NATO bag but too heavy compared to modern sacs.
I used run fell seams which where a night mare and seam taping wasn't available. I was breathable, weighed about 800g light for the time but bulky.

Now I'd just sew a plain seam, then follow it by top stitching on the upper edge, rain/water will flow over the seam. It generally not the stich holes water seaps in, but the gaps between where layers of fabric join. Top stitch also closed the join. Seam allowances are trimmed then iron on seal tape applied.

Tip# As you can't pin fabric, as you compromise the waterproofness. I use Prodec Low Tack Masking tape, to keep pieces in place.
This is better value & good enough Frogtape or Kleenedge are too expensive!https://www.toolstation.com/prodec-low- ... ape/p85936
(A few piece place where needed, like pins, rather than a long strip, easier to clean up)
Tape over the seam allowance it keeps fabric lines up. Or keeping a seam folded the right way for topstitching etc.

Notes on seams attached diagrams.