SYNTHETIC TOP LAYER FOR A WINTER MUMMY BAG?

[Eric Blumensaadt]

I’d like to get a synthetic “topper” for my down mummy bag so it, and not my down mummy, collects body moisture condensation. I’ll sew a 3″ wide mesh strip along the bottom so the frost can fall out when I shake it out in the morning.

I could cut down an Army poncho liner if necessary. Then I’d sew elastic bands on it to hold it on the mummy  bag and mattress. But it sounds too much like work. :o)

I know Enlightened Equipment makes synthetic quilts but they are too spendy for my purposes. So maybe a cheap Chinese knock-off?

[christopher witter]

I found this at Discovery fabrics . I took the dimensions of the poncho liner and created a summer quilt that could double as my winter overbag. It came out at around 19oz. All I had to do was throw some snaps on it, sew two channels, and hem the edges. Only took a few hours to make.

[Eric Blumensaadt]

Thanks very much Chris. This looks very good for a sleeping bag topper and very light but durable.

I went to the site and watched all 3 videos on Polartec Alpha and Alpha Direct.  I’m going to try to get some Alpha Direct that has the light ripstop already on one side then buy some light untreated ripstop to sew on the other side. I’ll sew it lengthwise about 6″ apart so I can more readily shake frost from it by leaving each end open.

That’s the plan. Hope it works B/C this stuff ain’t cheap at $35./yard plus lining material.

[Bill Budney]

One layer of shell may be enough for an over-quilt. That gives a place for condensation to form, while being extremely breathable on the other side (presumably the inside).

[nunatak]

Bill is right. From our testing an Alpha overbag is working best with a single layer of about 40cfm 10d ripstop to the outside. Sandwiching the Alpha between two layers and the condensation may form on the inside of the inner layer of ripstop, and that’s not what you want.

[Monte Masterson]

Timmermade offers Alpha Direct overbags with just 1 layer of Argon 67 but the wait time is 12 weeks.  $170 however it would probably cost you $130 in materials and shipping to make it yourself anyway. The overbag is rectangular and measures 58″ X 79″ and it already has the components you need to effectively secure it around your down bag. https://timmermade.com/product/alpha-direct-4004-overbag/

I made one virtually the same size with Alpha Direct 4004 and 1 layer of Argon 49 mainly to use as a summer quilt or blanket. Like the Timmermade it has drawstring head and foot as well as fasteners for elastic straps. Kam snap footbox.

If you want to go the inexpensive route Apex 2.5 and Argon 90 would be nearly impossible to beat, however you would of course need 2 layers of nylon with the Apex instead of one. Dutch sells slightly heavier 20D shell materials that are even cheaper.

[Jerry Adams]

you could buy a fleece blanket from amazon for $20

it’s 9 ounces/yd2.

cut it down to 1 yard x 2 yards – you don’t need to finish edges

18 ounces for an overblanket – kind of heavy and bulky to pack

[Marcus]

This has a great firsthand account of the pros/cons to apex vs alpha over  bags.

Alpha better than apex for over-quilt? My thoughts having made both
byu/eeroilliterate inUltralight

[Jerry Adams]

what is the loft of alpha direct vs apex?  and oz/yd2 (or gsm)?

warmth should be proportional to loft

[Monte Masterson]

3 yds of Apex 2.5 at $7 per yd and 5 yds of Argon 90 (15D) at $7.50/yd is around $58. Argon 67 (10D) is $10/yd and Argon 49 (7D) $12.50/yd. But the Ion (20D) is $4.50/yd and weighs about 1.15 oz per sq yd. Of course the heavier fabric you use the less breathable it is. I don’t know how much difference the heavier nylon really makes though, that’s a question beyond my knowledge. https://dutchwaregear.com/product/ion/

I’ve read that Apex provides more warmth per weight than Alpha Direct, however I haven’t verified it and I’m not certain it’s true. The AD is certainly far more compressible than Apex and it supposedly dries faster as well. Or should I say it doesn’t retain hardly any moisture to begin with. Also Alpha Direct holds up better after repeated stuffings and doesn’t lose its effectiveness as much as Apex. Nevertheless, an outer shell is needed with AD for optimal thermal efficiency. It blocks wind, helps retain heat and protects the highly vulnerable Alpha Direct from snags. I used Argon 49 because it’s the lightest but it’s thin and may not be durable over time. Argon 67 is probably the best choice overall.

[Bill Budney]

90 gsm Alpha Direct is 2.6 osy. My well-worn shirt is maybe 0.25 inches thick, max.

2.6 osy Apex is 0.6 inches thick, according to RSBTR.

So Apex is going to be warmer per weight for just the insulation. You might need two layers of face fabric for Apex, so let’s call it 4.6 osy for Apex vs one layer; 3.6 osy for AD.

4.6 osy / 0.6″ = 7.7 osy per inch (Apex)

3.6 osy / 0.25″ = 14.4 osy per inch (AD)

So, even with two layers of 1 osy face fabric, Apex still wins on warmth:weight.

RSBTR sells Apex up to 10 osy, which is 2.4 inches thick. It would take ten layers of AD to achieve that much loft.

No matter how you slice it, Apex is warmer. However, Apex degrades when compressed while AD does not, AD breathes extremely well, and AD recovers quickly from being wet. So there are reasons to use AD beyond pure warmth:weight ratio.

 

[Jerry Adams]

that is the analysis I haven’t read on the internet, thanks Bill

for alpha direct they don’t give numbers like loft and how it compares to other insulations, just marketing phrases like

“Polartec® Alpha Direct is an evolution of the original Alpha insulation that eliminates the need for a backing fabric.”

and

“Alpha Direct has caught the attention of both bigger outdoor clothing companies and ultralight cottage gear makers with things like:

– High weight-to-warmth ratio

– Comfort across a wide range of temperatures

– Extremely fast-drying properties (we’ve seen it come out of the washer practically dry)

– Incredible ability to breathe”

polartec has this cool diagram

just making a new insulation that adds a face fabric is not revolutionary.  Apex has a just as incredible ability to breath and comes out of the drier practically dry.  And rsbtr doesn’t mention it degrades less when compressed.  Polartec only says it’s “durable”, they probably don’t want to talk about how synthetic insulation degrades when compressed.

I don’t mean any disrespect, I love rsbtr and polartec has good products.  I think there’s a polartec product that’s very similar to apex. It makes sense for people to like this product for it’s durability.

If you don’t include the face fabric with the alpha and you sew on a layer of fabric there will be more of an air gap between so it would be slightly warmer.  But having the face fabric might stabilize the insulation making it more durable.

Alpha Direct is 59″ wide so maybe you could use it as a top layer with nothing else – no sewing, you’d have to baby the insulation side.  You could at least evaluate the concept

[Bill Budney]

If the goal is just insulation, sheltered from wind, then AD can certainly be used without a face fabric; just like all of the pure AD hoodies out there. If you cut a head hole in your blanket-topper, then it can double as warm poncho, like Clint Eastwood. Or a poncho liner: Mark Verber reported using something like that on his Camino de Santiago trek.

AD doesn’t fray a lot, so you can leave the edges unfinished, or “trim” them with a flame or hot knife. Do it carefully, though, because AD ignites easily. Bonus: You could use a piece of your blanket as tinder in a pinch.

However, if the goal is to move condensation away from your down bag, then I’m not sure that an AD-only topper would work as well as one with a face fabric? It sounds as though Nunatak may have tested that.

[Jerry Adams]

AD has similar warmth per weight as fleece – it’s about half of apex, maybe a little worse

[Bill Budney]

AD is fleece, just a lighter variant. If 60 gsm AD is as warm as 100 gsm fleece, then AD has ballpark 40% higher warmth:weight. Price is maybe 8-10x higher, depending on where you shop. So you pay a lot for a small increase in warmth:weight.

However, AD also breathes more freely than denser fleece. That’s terrific for a base or mid layer. However, it is also why AD may need a shell in conditions when something like a grid fleece may not.

Yes, Apex is warmer for the weight, but there are other reasons to like AD.

[Jerry Adams]

but fleece doesn’t normally need fabric on the inside and outside

so confusing :)

thanks for the info

[Bill Budney]

AD is most commonly used just plain, without a shell, at least for clothing. No other fabric; inside or outside.

AD is extremely air permeable, which makes it great for active insulation. Hoodies are perhaps the single most common piece of clothing made from AD.

However, a windshirt can be a good idea in wind.

AD+windshirt weighs about as much as grid fleece, but the AD is more flexible.

My TLDR: If budget fits, then AD is a nice addition to an ultralight wardrobe. If budget is an issue, then just buy cheap fleece. It works almost as well, with only small penalties in weight and breathability.

In this thread, we are discussing a synthetic topper for a down sleeping bag, which is a different use case than clothing. In this case, there may be benefit in a layer of woven fabric to encourage condensation; I’m not sure. The shell is not necessary to block wind inside of a shelter.

If the woven layer does help with collecting condensation, then I would expect that effect to work the same way over regular fleece or AD.

[Monte Masterson]

“The shell is not necessary to block wind inside of a shelter”

More so with a solid inner, but cold drafts are hard to eliminate. And when you look at how light many shell fabrics are compared to the Alpha Direct, a single added layer of nylon is easily worth the weight. AD combined with a UL nylon shell is more than the sum of its parts (thermally). Alpha Direct looks porous to begin with and I couldn’t imagine not having a shell with it as an overbag (or summer quilt). Again, AD is so vulnerable to snags that fact alone could justify a single layer of nylon. Nunatak and Timmermade extoll the virtues of an outer shell combined with Alpha Direct, and of course they’re professionals who’ve field tested a lot in order to come up with their ideas.

Keep in mind that an overbag also serves to wrap around like a blanket when sitting around camp. You definitely want an outer shell in that scenario because there are of course potential snags galore. You also want the wind blocking which is provided by the nylon shell.

 

[Bill Budney]

All great points, Monte. I was just trying to respond to Jerry about the differences between AD and regular fleece, but you’re right, of course, that there plenty of good reasons for the outer shell.

Plus you can carry both layers for about the same weight as regular fleece.

[Stephen Seeber]

I took a quick look at this thread.  There is a fair amount of discussion of warmth to weight performance of high loft, fleece and Alpha Direct.  I have published lots of information on these, using clo/oz or clo/oz/yard.

You can find information on high loft here. Table 5.  High loft insulations range from .24-.59 clo/oz.

You can find information on fleece here. Table 3.  Fleece insulations range from .05-.12 clo/oz.

You can find information on Alpha Direct here. Table 3.  Alpha Direct insulations range from .14 to .22 clo/oz.

I use a synthetic top when it is really cold, like below zero.  I use a 40F EE quilt that weighs 18 oz. This uses 4 oz Apex.  The R value of 4osy apex is about 1.9.

In order to match the warmth of this quilt you would need  2 layers of 100 weight fleece 9180.  Two layers of 2 square yards would weight 38oz. The warmth would be 80% less than that provided by the EE quilt.

In order to match the warmth of the quilt with Alpha Direct, you would need 5 layers of 60 gsm.  This would weight about 20 oz.

Either the fleece or AD option would take up an immense space in your pack.

The real issue is how much extra insulation do you need on top of your sleeping pad to move the dewpoint completely out of your sleeping bag and into the top cover.  I didn’t do much calculation on this when I purchased my quilt, but I doubt a single fleece or AD layer would do it.   I think anything less than a 50F rating for a top quilt may leave you disappointed, particularly for a long outing.  I have not done a long outing with mine, but I am curious if anyone has tried multiple nights in sub zero F temperatures with either a fleece or AD overlay.

 

[Jerry Adams]

So, AD is quite a bit better than fleece

As far as moving the freezing point out of your sleeping bag goes, another factor is the air layer just outside your bag.  If you’re not camping in wind.  (If you’re in a tent then there won’t be any wind).  There’s about 10F temperature drop across the air layer.  For example, if it’s 10 F ambient, the outside surface of your sleeping bag will be 20F.

So, the top quilt doesn’t have to be quite as warm.

[Monte Masterson]

By comparing Apex 2.5 of an EE 50 (13.6 oz) and DIY AD/Argon 49 quilt (11 oz) in summer field testing, I’d say the EE quilt’s lower comfort limit is around 53*F, whereas I’d rate the AD near 56*F (w/ base layers for both). Just a guess mind you. Point is I believe the warmth to weight ratio of AD is closer to Apex than what many people think. And Alpha Direct definitely packs down smaller for its weight.

AD 4004 and Apex 2.5 weigh the same. I maintain the warmth provided by AD 4004 is about 75% that of (same weight) Apex, regardless of loft measures. US Special Forces put a lot of money and research into the original Alpha (which needs a double shell). Alpha Direct then comes along and doesn’t even need an inner shell. It’s amazing stuff.

Bulk and losing effectiveness after repeated stuffings are Apex’s biggest drawbacks. And the fact that Alpha Direct only needs a shell on one side (as an overbag) means less weight and more breathability. Also needing only one shell compared to 2 edges AD closer to Apex in warmth to weight because of course nylon isn’t nearly as thermally efficient as insulation. However 1 layer of light (10D) nylon for an outer is ideal IMO.

I’m sure a lot of MYOG’ers might opt for the heavier (4 oz) Alpha Direct 4008 when making an overbag, and I could definitely understand. https://ripstopbytheroll.com/collections/synthetic-insulation/products/polartec-alpha-direct-4008

[nunatak]

To push a quilt into colder seasons it doesn’t work for me to layer it with yet another quilt, whether Apex, Alpha or down. The drafts and cold air exchanges from the top and underside is what puts a limit to my quilt use.

Using a traditional backpacker’s bivy can help, but the generous size and massive ‘hoods’ does not really cut the draft issues for me.

So for a 15 day trip in November I made a hooded and center-zippered mummy over-bag using Alpha 4004 and 7d Argon 57 nylon taffeta shell. The hood is small and form fitting and the bag itself is carefully sized and sculpted with compound curved panels to fit perfectly without crushing the loft.

It weighs 11.2 ounces and worked quite well. Also super compact at about 10″ L x 4.5″ diameter.

The coldest cowboy camping was mid/high teens. My hood-less down bag is rated 28°F. I wore base layers – doubling up on the top – and even with the 11 hour nights I was comfy enough to not wanting to change much.

Breathing into the Alpha lined hood moved the condensation away from my face and saved the top of the down bag from getting damp. I’m sure my bag absorbed some body moisture over the course of such a long trip, but I never felt an urgent need to dry it in the not-so-powerful sun; even with a layer of frost on the outside of the Alpha over-bag.

View post on imgur.com

[Stephen Seeber]

AD 4004 and Climashield 2.5 are a good comparison because their weights are about the same.

Here is how they perform.

It’s pretty clear that the CS 2.5 has 3x the loft, more than 2x the warmth, and almost 3x warmth per weight.  This will change somewhat because CS needs to be sewn into fabric.  Because it does not have to be quilted, it can perform a little better on warmth when covered but will lose some MVTR (as long as you don’t lose loft).  On the other hand, you could take two square yards of 4004 and throw it over your bag, secure it with elastic straps, and get most of the benefits of the AD, assuming you are in a tent that blocks the wind and you don’t need the greater warmth of the CS 2.5.

Now, this all misses the key point: Can these provide enough warmth to move the dewpoint/freeze point out of the bag/quilt?  Unless this is established, speculating which material is better is just that. The summer performance of an overlay is irrelevant to your actual winter camping conditions. The answer, of course, depends on the ambient temperature, the loft, and the thermal performance of the underlying bag/quilt.  If you know these things, you can pretty easily calculate the R-value required to move the dewpoint into the over quilt.

 

[Bill Budney]

For a multi-day trip, you’re eventually going to have to dry whatever gets wet, right? Whether down or synthetic, topper or just your regular bag/quilt; that’s why one side is a dark color, so that you can spread it in sunshine to dry.

I can see how shaking frost off of an AD topper would be an advantage. For a topper with two shell layers, what is the practical advantage over just drying your regular bag? (Other than extending the temperature range, of course).

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