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Cuben/M50 Borah Bivy modification completed and tested :)
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Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
Cuben/M50 Borah Bivy modification completed and tested :) on 05/18/2013 12:35:00 MDT Print View

Finally got around to doing it, and it worked out great!

Had a big vent cut out of the bivy to help eliminate condensation, and only put a whooping 3g onto the weight.

Long live the tarp/bivy combo!

Pics and more info can be found on my blog here:

todd h
(funnymoney) - MLife

Locale: SE
Re: Cuben/M50 Borah Bivy modification completed and tested :) on 05/18/2013 12:39:09 MDT Print View

Very nice, Cesar!

Hadn't thought of that one before. I might not have traded my last traditional bivy if I had seen your post!!!

Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
Re: Re: Cuben/M50 Borah Bivy modification completed and tested :) on 05/18/2013 12:59:35 MDT Print View


You could always get another bivy. There are a lot to choose from, but I say if your tarp/bivy combo gets past around 500-600g, you might look into hybrid tents--unless you just have to have the flexibility that the t/b combo offers.

A 353g fully enclosed shelter system that can be used together with trail shelters and/or cowboy camping, that offers solid protection against bugs/critters and rain/wind, and that as little/no condensation is pretty awesome if you ask me. :)

Looking forward to a lot of comfy nights out this summer season!

Brian Johns

Locale: NorCal
Fantastic on 05/18/2013 13:05:42 MDT Print View

That is awesome Cesar. Much better than what I pictured the times you have mentioned it. Just send me your address, and I will post my M90 bivy to you to modify. PayPal okay?

Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
Re: Fantastic on 05/18/2013 13:20:47 MDT Print View

Ha! Sorry man, kind of you to make an offer, but I am not in the bivy modding business, plus I live in Sweden. I say just take your bivy to a local seamstress and get it done. There are several good options for the vent fabric, I just stumbled upon a very good one, but you could order some noseeum net from several places like Zpacks.

So M90 doesn't breath well either, huh?

Jason Elsworth
(jephoto) - M

Locale: New Zealand
Cuben/M50 Borah Bivy modification completed and tested :) on 05/18/2013 17:54:24 MDT Print View

Great idea. I am going to get my local sewing shop to do this for me. The Zpacks bivy has something similar, but with an option to cover the vent.

Michael Geoghegan

Locale: SoCal
Cuben/M50 Bivy Modification on 05/28/2013 14:49:43 MDT Print View

Perfect finding this! I was just toying of doing the same with a M50 & .51 oz/sqyd Cuben bivy I made last summer. Works great and is super-light but the M50 just doesn't breath enough. Condensation every time.

Time to dig and see how much No-see-um netting I have left.


Brian Johns

Locale: NorCal
Re: Re: Fantastic on 05/28/2013 15:29:13 MDT Print View

"So M90 doesn't breathe as well either, huh?"

Well, likely a little better than the M50 - and in a quilt I am generally fine enough, but in a sleeping bag ... yeah ... it's a bit damp at times. Nothing that does not dry out, but I can see where it'd be a problem on a cold enough night.

Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
Update on 08/16/2013 01:40:45 MDT Print View

Just wanted to give an update on how the bivy is doing in the field after testing it out again. Here is a pic if it in action:

I opted to sleep on the tip of a peninsula of a big lake, and with pretty clear skies I decided to cowboy camp it. It was awesome. As the sun went down the midges and mosquitoes came out in full force, but I lay safe and cozy in my bivy after a nice swim. I could see a small cloud of bugs over my face as I slipped into sleep, behind them several stars peeking through the dusk.

In the morning there was a fog over the water, and I had expected this location to be the place to give me condensation issues, but there was hardly any. At first as I inspected the inside of the bivy near my torso I thought that there was none at all, but when I got up and turned the bivy inside out, there was just a touch of dampness at the very tip of the foot box. Not enough to form drops of water, more like a fine mist, and again--this was only in the very tip of the foot box and no where else. It was dry in a matter of minutes.

So still very happy with the mod, and my bivy/tarp combo is still my go-to shelter for trail hikes. I think that all bivy sellers should have an option to add a vent like this as a standard option.

Joe S
M90 vs M50 on 08/16/2013 07:21:02 MDT Print View

I have an M50 bivy that occassionally has condensation issues. Can anyone who has used both fabrics opine on how much "better" M90 breathes?

John West
(skyzo) - M

Locale: Borah Gear
Re: Update on 08/16/2013 09:07:47 MDT Print View

Awesome job on the modification Cesar, looks really good! I'm glad it is working out for you.
The M50 has changed over the years from when we first started making these bivys, and the newest runs in 2013 are seemingly not as breathable as the previous ones. Most people these days (90%+) order the M90 anyways, but I'm thinking about making a vent like this standard on the M50 ones so people can still enjoy the light weight of a M50 bivy. The people that buy M50 these days tend to live in dry climates and have no issues with condensation.

As far as M90 goes, it is very breathable. Very few people have condensation issues with it, and it still has great water repellancy. I've found that with the couple people that have contacted me about the M90 leaving a small amount of condensation, just tying off the head net (use shock cord) to increase air flow got rid of any issues.