Expander wedges and down quality?

[Moondog55]

I have my OP Cocoon sleeping bag and it is quite good and with the overfill [ an extra 150 grams of 800+ down] rated to about -18C Male [ or approximately -11F] but if I was actually going someplace really cold it wouldn't be warm enough.
I have another sleeping bag from Macpac, a Large Dragonfly rated to -3F and to -10M and with an expander wedge I could easily fit the Macpac bag inside the Cocoon and use it as a double bag.
Bear in mind this is a mainly theoretical query; but OP only do a -10C rated wedge filled with 700FP down and I am wondering if the difference between a -10C rated wedge and a -18C bag would be noticeable in real world conditions?
I have in the past asked OP if they could use 800FP down in the expander wedge to get a lower temperature rating but when I asked a couple of years ago they wouldn't do it. I don't know why.
I notice that Western Mountaineering don't do a winter rated expander wedge either and wonder if there is something in the way these work that limit how much girth you can add without compromising a sleeping bags design?

[Moondog55]

Has anybody tried to or actually made an expander wedge them selves?

[stry]

I know two men who ordered and used OP wedges. I never heard any complaints, but that isn't what could be called a meaningful appraisal.

Whatever you do, the weak spot is going to be the sides of the wedge, and I doubt that trickery such as flaps/baffles would be 1OO% effective is eliminating these cold spots.

I doubt that the outcome would be worth the faffery, and I would simply buy the OP wedge, use it, and if necessary put the thinking cap on for enhancements.

Provided there is sufficient fill, I would be unconcerned about the difference between 700 and 800. 700 will be fractionally heavier for the same loft, but again, if loft is identical, discerning any difference in warmth, if any exists, will be a challenge.

[Moondog55]

Thanx Stry
My problem is that while the expander has a rating of -10C the sleeping bag is overfilled and rated at -18C.
OP tell me they now [ as of this year] use 800FP but reduce the fill weight to get the same rating; won't add extra due to minimum baffle height so the wedge baffles must be less than 25/30mm
I do feel the cold much more these days; especially when getting out of bed in the middle of the night to pee; which is why I like to sleep in at least a minimal warm clothing layer.
Yes I do have pee bottles but it's getting harder to use them due to old mans problems.
Otherwise I'd continue to use my UL overquilt; the boost of which is great enough that any more than base layers becomes too warm with this sleeping bag.

[stry]

I get, and empathise with, all that MD.

Is 8c over the area of the wedge going to lower the in use comfort of the bag by much ?

Try it and see. If its a problem just layer up, or stuff a jacket or some thing similar in against the wedge.

[Moondog55]

Thinking about it over the last few weeks I'm now of the opinion that the money would be better spent on another LW overbag.
But it would be a DIY project and would have to be warmer than the Nunatak overquilt.
Still very much a theoretical exercise tho but I have bought some UL fabric.
Simply layering my S2S Traveller over the top doesn't seem to be the way to go as the heavier S2S does compress the Cocoon a lot, the Cocoon being less substantial than my old summit bag.
The Old Ultra bag is warmer but I find wriggling in [ and wriggling out in the early hours even more so] hard these days.
Car camping would be no problem, weight is of little consequence in a vehicle.