Ascentshell vs Event vs Pertex Shield CFM/Hydrostatic head? (Bivy choice)

Can anyone help? :)

I have no experience with the OR fabrics, but I do have experience with EVent, and have found it to be a very good fabric for uses like a bivy.

I have an old Early Winters Goretex bivy (1978) very similar to the Rab Alpine Bivy, and have used it in the manner you describe you’d like to.

Given the 3 different designs you posted, and given your use criteria (summit/ridge sleeping), I’d get the RAB. There’s no way I’d want to fiddle with and try to stake-out the little hoop structures on the OR models above timberline in windy alpine conditions. Less fabric flapping in the wind is better. When it comes to bivy’s, follow the KISS principle.

Would add, the OR models seem more suited for bike-touring and woodland overnights, not windy summits and ridges. While undoubtedly any of the fabrics would work, I think my focus would be more on the bivy’s design than its fabric. Having said that, in the Rab you have a great fabric AND a good design alpine environments.

For what it is worth I used the Rab Alpine. Breathability was very good (still had slight condensation) but I ended up selling it because it has a very significant mummy cut so after I long day of backpacking your legs have to be held together. If I were doing it again I would look at the Ascent which is a slightly roomier cut and has a bugnet. The Alpine has a slightly more breathable version of EVent than the Ascent but the space would be worth it for me

http://www.eventfabrics.com/products/#waterproof

I think the Alpine is DVStorm and the Ascent is DVAlpine

Here are some numbers from my measurements.

Event ( I have had access to only one version of this fabric, so I don’t know how it corresponds to what is used in your product.) HH:30000+, CFM:.58, MVTR: 2910.

Ascentshell (OR Skyward II) HH:16170, CFM:1.23, MVTR: 3060

Pertex Shield (OR Helium II, 2019  HH:18280, CFM:<.43,MVTR: 1500

Of course, we don’t know the extent to which any of the fabrics in your products might vary from the fabrics I tested.  Based just on these numbers,  the eVent might be the best choice.  However, these numbers do not consider design difference between the various actual products.

Thanks for the answers guys!

The hoop is not a problem in high winds, a friend of mine had a similar bivy and due to the low profile wind is really not an issue with a hoop.

Stephen, didn’t you mean Ascentshell is the best choice based on the numbers? Looking at CFM and MVTR, why is Event a better choice?

I believe CFM is generally irrelevant for any of these because they are all very low.  The important numbers are MVTR and HH.  MVTR are so close between Ascentshell and Event that I would rate them as a tie.  The big difference between the two is HH.  The Event has far more resistance to water penetration.  Now, the most vulnerable component to water penetration is the floor because it is subject to high pressure from kneeling or other actions you make take inside.  In each, they use a coated nylon fabric with heavier denier. So, Event and Ascentshell are removed from that portion of the performance equation. That said, the Ascentshell is probably adequately waterproof for most wind driven rain although at extremes of wind, when you probably don’t want to be out in a bivy, the Event should provide better protection. Your decision will look not only at the fabric characteristics but also incorporate  weight, design features, interior space, cost and other relevant variables.  So, your decision might not be the same as mine.

Thanks for the clarification.

I’d like to try both of them, however, it seems that the Stargazer Bivy is discontinued according to some resellers.