No tarp?

Yeah, you could go with just a bivy, no problem.

There are a few eVENT bivies made by integral designs at around 18oz, but I dont think they have bug netting, but do have the best breathability by far.

there are also 6-8oz bivies from montbell with no netting, but with a head net, they would be the lightest option.

REI has a minimalist bivy at 15oz with bug netting, looks good from what I saw at the store, but it may not be that breathable

There are also great bivies at owareusa.com at about 18-20oz which come in either eVENT or Gore tex waterproof tops

also available at REI, there are two 18oz bivies from mountainhardwear one goretex paclite, and the other Conduit SL™/nylon.
and the outdoor research basic bivy would be a good option at 20 oz

But if I were you I would go for the lightest montbell bivy, I have one, the wide and long is huge, even big enough, to store some gear, all you have to do is get a cheap headnet, and cover the face opening with your rain jacket, and you have a ultralight, breathable, simple shelter.

Is the problem with silnylon and other light bivys that they can’t really withstand a rainshower/storm? If a light tarp is 8oz, can a get a solo shelter bivy that’s under 15oz? I can always add bug netting etc if I make my sister sew it so that alone isn’t a deal breaker.

Would it be different if I had a synthetic bag vs down bag? I can deal with some discomfort as long as I’m warm enough to safely sleep for a few hours before riding on.

Silnylon really can stand a rainstorm. But you wouldn’t want to use it for the top of a bivy becasue of the condensation that would occur.

You really need a small silnylon or spinnaker tarp over the bivy unless the bivy is made of a true w/b fabric.

Ideally, one of the BMW bivies that were sold on this sight would be perfect for what you have in mind, being very light and having bug netting and the ability to stake them out. They would work fine in light rain and very well under a tarp in wet weather. Most models weigh less than the emergency bivy you are using now.

Unfortunately, they are all out of stock at the moment.

The Oware bivy on this site seems to be in stock and is only a few ounces heavier.

If the only objection to the tarp is carrying poles, I’m wondering why you can’t use your bike to build a shed-roof rig or one end of an a-frame. If the other end is very low you could probably get away with using the bike pump to support the other side of an a-frame too.

Me? I’d probably go with the Oware bivy (since the BMW Nano is unavailable) and a small tarp in a shed-roof configuration. That and four stakes and you’d be pretty golden in pretty heinous weather.

Probably the lightest, true waterproof breathable bivy shelter would be the montbell breeze dry tech UL sleeping bag cover. It can withstand a rainstorm, you need something to cover the face but a rain jacket will work,
with a light headnet, this will only weigh 6.5-7oz total
and you dont have to set up the tarp, just put your bag in and then get in yourself

again, you may not choose this, but it is the easiest and lightest way even lighter than a NANO tarp/bivy combo

Thanks for the comments! I’m going to check one out(montbell) and perhaps do some light mods if necessary to get exactly what I want.

My biggest objection to the tarp is setting it up, more effort when I’m “falling asleep on the bike tired” (literally). If I can roll out a bivy with my bag already in it, throw in my pack and pad and climb in it’s just plain the easiest. Plus carrying poles on the bike if they are longer than the top tube becomes difficult due to the technial riding. Do the BMW bivies really work without a tarp? They (the ones I can view at least) say they are designed to work with a tarp as well.

I will be already carrying a rain jacket so perhaps the montbell with bug netting sewn into just the opening is still superior to the BMW bivies?

Oh and waiting for something to come into stock isn’t a big deal since I don’t have any multi day stuff for a little while. My emergency bivy works for now and I have some time before I need a new setup. I just worry that the emergency bivy just isn’t quite up to handling worse case conditions in the future.

Re.BMW bivies without tarp

The BMW bivies will only work without a tarp in light rain, they are only water resistant, and in a heavy or long rain water will soak through

If you expect little or no rain, you could make the bivy work.
But if you expect “real” rain, I would go with a waterproof breathable bivy sack

BTW, I recomend using any bivy with a ground cloth to keep it from ripping or being punctured by rocks, twigs, or other objects. cut down space blankets work well.

That’s what I thought. I don’t expect long or extended hard rain BUT it’s possible if I get stuck up high (broken frame/wheelset/etc). In that case I’d be really pissed I sacrificed my waterproofness for a couple ounces. Please keep any comments and suggestions coming. I definitely don’t come from the background most of you do and I’m trying to keep an open mind and learn as much as possible.

I slept recently through an unexpected night of light rain in an Oware bivy. Keeping my nose near a few inches of open zipper was annoying, but not a survival problem. Since I was on open snow suspending the top was not an option.

Above treeline my preference is a two-hoop bivy. I used an OR for a long time successfully, but now am using the much lighter Black Diamond Lightsaber. It doesn’t sound like it fits your preference, since it weighs about 24 oz and has a 15″ long pole bundle, but it is quite comfortable for avoiding rain, wind, and bugs with a very quick setup such as you describe. You could also decide whether to bring the poles depending on the weather you expect.

Below treeline I recently used the Oware again, with an A16 hooped bug net, total weight ~14 oz. Very comfortable for bugs in non windy conditions, with the option of a less pleasant night if it rains and you don’t put up a tarp.

Whatever the type, some kind of bivy sack sounds good for your needs. A good compromise might be a single hoop bivy. There are lots of choices out there.

Is there a true waterproof breathable fabric available for a DIY construction project that would be suitable for a bivy top? I’m still looking at buying the Montbell bivy but if the same or similar fabric was available it would save me from hacking the bottom off something brand new…

Just a thought – you may think it too primitive.

Why even carry a bivy? I have a patagonia dragonfly pullover and some montbell UL windpants. Add a bug headnet and some Seal Skinz socks and you have a highly water resistant and breathable insect-proof shelter that you can ROLL OVER IN and WALK AROUND IN.

If the purpose of a tent/tarp/bivy is truly to protect you from wind/rain/insects, then I propose that you are already carrying that kind of protection in the clothes that you carry.

Interesting idea. I would have to put some further thought into it.

My biking clothes do not have much rain protection though. I typically wear standard jersey/shorts with arm/knee warmers for cold and a light jacket for wind. If I get wet, I get wet, and usually in the summer that’s not a big concern with drying off until I was done riding. Then I could grab a dry base layer shirt and socks and climb into my “sleep setup”. I do relish the idea of “getting out of the weather” even if it’s just crawing inside a cuben fiber bivy with the face upside down in bad weather and pulling a bivy around me at night.

Your suggestion does get me thinking however and I may ponder it a while and see what I come up with. I’m trying to find more info on what adventure racers do and use since this stuff is similar albeit with no checkpoints or support of any kind allowed.