Cuben/ Silk/ Momentum hybrid S/bag Bivy

What about tucking edges of the top to reduce air space when it's colder? If you could pull it off, I'd prefer a pad/bivy.

sounds good, all cuben.. a bit beyond my skill level maybe.

I was thinking I could extend the insulation down the vertical tubb wall somewhat (to mat level, i am generally wider than my mat : ( ). I'm really only needing down to say 0c (30f) including down clothes. Was hoping to just use 2.5oz climashield but ive never used a quilt. Tucking under is a good point, i guess a pad level baffle would defeat the top quilt weight reduction attribute.

Some thoughts:

Not familiar with silk as an outdoor fabric. Assume you are.

All the fabric-bonded-to-insulation bags I've had delaminated with washing.

If the construction does not cause the insulation to overlap the mat, heat will exit big time. My understanding from reading posts on this site is that this is why the quilt users attach their quilts underneath them in some manner or other.

Don't know what you mean by 'quilt'ing the Climashield. Thought it was stable enough to not require quilting. Seams through it will create additional points for heat to exit.

Are you sure you are VBL material? Some like it, but some like me would never be warm, or comfortable, in a VBL bag.

Not sure how you plan to get in and out of the bag.

You might attach the edges of the silk liner to the edges of the outer at the bottom corners and every few feet using loops and ties inside. That would stabilise the liner without bonding.

Ideally, the silk liner could be detached from the top quilt and bottom pad, so the only thing you would normally have to wash would be the liner. And you could bond the Climashield to the top outer without having to wash, and delaminate it.

You could add an additional layer of 7 D fabric as the top of the pad envelope – less than an ounce in added weight. The silk liner could attach to the sides and bottom of the envelope. Then you'd just need to figure a way to stabilize the Climashield without sewn-thru seams, and attach it to the bottom envelope in a way that does not allow a cold seam between the pad and the insulation.

You might have something there, especially if you have other good reasons to believe that the silk liner would be a plus.

I find these things as hard to write as read.

Might have confused things a bit, I havent used silk in a project but see it mentioned (for s/bags) recently here (?). Anyhow:

I was just 'considering' bonding, i though I saw where someone had successfully bonded baffles. Though, yes, washing was my concern too.

I didn't plan on any quilting, just the sewn (and or bonded) side seams.

In essence, what i'm banging on about is a summer weight sleeping bag with a waterproof base.

The daydream i'm having is a high cuben floor and mometum top for the shell, silk for the inner. I'm considering Climashield for the top insulation, down to mat level. No insulation in the floor/base, just a pad sleeve formed between the Cuben and silk.

It wouldn't act as a Vapor Barrier.

I could make a quilt but like an enclosed bag, the idea seems to offer a highly breathable bag with a waterproof base and water resistant top. I'd likely put a short zip somewhere (down the middle?) on top to open it up, perhaps a 'hatch' in the top at the foot section.

Thanks, i'll read back through your other thoughts, good stuff!

Check this out from Mr. Bill Fornshell……Ahead of his time!

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=4262

Great find Todd, iv'e gleaned Bills projects but somehow missed that one. Yes! very similar to both those in one (with a single layer of 2.5oz climashield XP insulation.. perhaps I could add a second layer of 2.5oz insulation in winter.. (built in the same way as Bills quilt here) ) Thanks for that!!

Someone mentioned the durability of silk when wearing clothing in a sleeping bag (on another thread). I didn't notice any tearswhen i first read this but had a closer look at a Sea 2 Summit Silk liner that has been used this way (with soft montbell inner jacket and pants). Not sure if it would have happened regardless but the fabric is covered in mini tears/pulls seen when held up to the light..

I would love to see this put together. I have been toying with a similar idea for quite some time using WPB fabric for areas with pleasant weather as a standalone shelter. A few things you may consider:
*silk is not ideal for a quilt/sleeping bag. It is less durable than similar weight nylon and more hydrophyllic. I would give it 5/10 for usability. It isn't terrible and may work well in an enclosed sleep system like you plan though. In my quilt, it had more exposure than your system would have. Some of the light nylons available now (OWFinc has some inexpensive stuff) may suit you better. The silk can be super light though if it stays dry.
*bottom layer of fabric inside the tub floor may not be needed
*I'm not sure how the bonding or sewing the liner to cuben would work, but I would love to see it done successfully. Steve Evans at Suluk 46* may have info on what would work best. He made a cuben/momentum winter shelter and stitched the two panels together. Maybe cuben tape could be used as a seam sealer.
*the warmest thing to do concerning the insulation edges and sleeping pad are for the insulation edges to get between the pad and you to prevent drafts and reduce open space you have to keep warm. Maybe have the pad outside the bag to facilitate this. When I made my best topbag (of 4), the bottom layer was between 12 and 16" wide for this reason and proved to be about ideal. The RAB Topbag from back in the day was a failure due to the 22" wide bottom panel and narrow insulated top section.
*hand washing should be fine. synthetics can be air dried too
*the area where insulation has a cuben shell could get damp, but probably not too bad

Are you going to make a hood too? bug netting like a bivy? This is an exciting project!

Thanks for your thoughts, you seem to have your head around this.

I'm still not decided, i respect the way other people have approched this, usually ends up with the thought process leading to the way things have been done by most.

I'm planning to use this under a shelter so the cuben base is more to seal against wind/boggy ground just with the idea of making a bag as waterproof as possible without forming a vapor barrier.

I was thinking of finishing the base as just a tubb at the head end (similar to Bills bags, a bit deeper)

The lower part where the insulation comes down into the cuben I was thinking something very breathable (like silk) would manage the ventilation well enough from the inside (finding a breathable way to bond might be a bit tricky..)

I see the thinking behind quilts in that needing to wrap the insulation around so far (to bring it down onto the pad) almost achieves an everyday sleeping bag (not much weight saved) but I do like the idea of a sealed floor.

I'd be likely to strip down to jocks in warmest weather so baulk a bit at sleeping straight on the cuben (hence the silk ideas)

Its almost sounding like a bivy shell plus snap in quilt would be more versatile.. i guess eliminating layers of fabric is the goal with these things. I too find it interesting, i'm not really settled enough on one particular idea so I appreciate everyones input.

Thanks