Well, my English is surely not faultless.
But so far I understand the following sentence right, your sleeping bag is a
summer sleeping bag:
"This model has been tested extensively for more than a decade in various environments around the world, and remains the
summer bag of choice for both Ray Mears and the Woodlore."
Also the above mentioned time between late spring and early autumn I rather would call the
summer and not the winter, regarding German circumstances of course. No idea how it's exactly in Britain.
And in this context the mentioned -15 °C is the extreme temperature rating. At - 16° you perhaps would lose a few toes or an ear or the tip of your nose perhaps, or you could die if in bad shape. With bad luck that even could happen already at -15°C.
But only if you use a good sleeping mat or other ground insulation. Otherwise you will probably get far earlier in serious trouble.
If you look at the temperature ratings of sleeping bags, the temperature comfort or temperature women is the rating you have to look at, and don't forget that they always assume that you wear a merino wool suit or something similiar in it. Most people don't realise this if they are looking for a pure summer sleeping bag!
If the temperatures reach the by Snugpak called
low point or elsewhere callen
men
it starts to become unpleasant in your sleeping bag, but you still will sleep if you are tired. Below that your body starts the battle against the cold if you don't wear in it an additional serious insulation like a padded army suit and triple socks or tent boots that are padded socks for your feet.
That additional clothing worn in the sleeping bag would lower the comfort of it is a cold war era NATO myth. They told it in the conscription armies when they issued the cotton field uniforms. If you get moist or whet in such clothing you have to put it off before you enter the sleeping bag of course. But if you change into a dry uniform before you enter the sleeping bag it will become warmer of course. And especially it becomes warmer if you wear dry fleece clothing, padded clothing with polyester or down filling or wool.
Wool doesn't transport moisture better outside than cotton or linen by the way but generates heat if a bit moist.
Down is pretty risky in whet cold weather conditions and also in colder conditions if you use it wrong.
British bushcrafters are surely served the best with polyester fleece clothing and padded suits with polyester hollow fibre filling and also so filled sleeping bags. That's the stuff that's made by Snugpak in Britain and also offered by Carinthia.
Both brands deliver their products to several NATO armies. They are the market leaders in Europe and great competitors.
The imported Snugpak stuff is rather meant for seldom recreational civil use and made in a cheaper and lower quality, the British made Snugpak products belong to the best of the best one can buy and are surprisingly affordable.
Carinthia products are always high end products, but the military equipment is made a bit more durable than the also by Carinthia offered civil stuff.
I recently called Carinthia, spoke to a specialist there and asked a few special questions about their products.
Expensive equipped armies issue the Tropen that one can put into the Defence 4 to achieve a winter sleeping system for really cold weather. That's constructed for Austria and Bavaria and for the eastern NATO border, probably a bit overkill for recreational camping in Britain. You don't need to carry a sleeping system around that's constructed for Alpin winter conditions or the Polish-Ukrainian border. It's very comfortable of course if you use it at -10°C, but it's like the Snugpak Special Forces system rather meant to use between -15°C and -20°C and with padded suit inside even until -25°C.
They issue with it 110 litres rucksacks. Would you put it into your 60 litres rucksack it's more or less full, depending on how you pack it exactly.
The Defence 4 fits over the Tropen, and regarding the fabrics they are made of that's the optimal combination. That's issued in the German army for example.
But you also can put the Tropen into the Defence 1 or the Defence 1 into the Defence 4 if you want to. And originally belongs around it the Carinthia Goretex Sleeping Bag Cover with central zipper.
As I assume that you don't plan to spend this winter in the woods at the Polish-Ukrainian border, I recommend to try out first the equipment that you already own!
If you own two sleeping bags that fit well into each other, you inside and all that into the bivvy bag, without compression of the filling if in use, you can count the weight of your relatively new relatively expensive sleeping bags together and compare the result with the weights of winter sleeping bags that are offered by the same maker. Your added weights have approximately the same insulation value like a winter sleeping bag of the same quality and weight. If they don't fit perfectly into each other they are perhaps a bit less warm, depending on if you compress the filling or not when you use it.
1700 g Ray Mears summer sleeping bag
+ 1050 g Defence 1 (Size M)
--------------------------------
2750 g together
1700 g Ray Mears summer sleeping bag
1200 g Defence 1 (Size L)
---------------------------------------
2900 g together
The Carinthia Defence 6 weighs 2600 g (including one large compression bag of approximately 250g) and is rated to -18°C comfort temperature.
The Snugpak Special Forces complete system (SF1, SF2 and adapter) weighs 3200 g (including 3 slightly lighter compression bags in different sizes) and is rated to -15°C comfort temperature.
You have here more zippers to carry and 4 shell layers instead of just 2 and that gives you a bit less insulation than the same weight in polyester hollow fibre filling although insulating air is also trapped in between the both sleeping bags. But otherwise is the option to open only the outer bag a bit but keep the inner one fully closed very comfortable because you can adjust like this very well the temperature inside your sleeping system, what's very interesting if you use it somewhere between 0°C and -10°C and absolutely worth it in my opinion.
One single winter sleeping bag also can become too hot to use it! That's one of the reasons why the NATO armies issue such modular sleeping systems.
Should Your Defence 1 fit well into your Ray Mears sleeping bag or the Ray Mears sleeping bag well into your Defence 1 and all that into your Snugpak bivvy bag, you should try out that before you buy anything else!
I guess that one will fit into the other and assume that both in each other and the bivvy bag around it will serve you all together comfortably until approximately -15°C if you use that on a well rated sleeping mat.
If that generally works well but isn't warm enough yet I would rather buy a padded army suit like Carinthia LIG or a British made Snugpak suit. Or even, if weight doesn't matter so much, a relatively new but used Dutch or British army military surplus suit like that for rather rare occasions.
If both sleeping bags fit into each other both ways, you should try out if you can blow easier through the outer fabric of one of them, this would become the inner bag.
And you should try to put an equal drip of water onto both outer fabrics and look into which the water sucks in later, that would become the outer bag.
If you need a new compression bag, I recommend to buy the
large Carinthia military compression bag.
www.carinthia.eu
It's simply the best you can get.
With the 7 compression straps you can get your sleeping system in every sensible shape in order to fit it into your rucksack. And this you can also attach well onto your rucksack if the rucksack is constructed to do that. In this case you could put a Snugpack DrySack 35 litres into it, that you close after pressing the air out of the Sleeping bags, or you simply put the dry bag around the compression bag. The latter is less protective but a bit easier of course.
I think that your Snugpak bivvy bag and your both sleeping bags fit well into this compression bag.
It's made for Defence 4 or Defence4 and Tropen together or the Defence 6 but the complete Snugpak Special Forces system including SF bivvy bag fits in there very well too, even with additional British army Goretex bivvy bag.
I think you should try that out first, the chance that it fits and works well is pretty high.
If it doesn't work well, come back here and we can talk about which new Carinthia sleeping bag would be the best choice for you. But currently I guess that you don't need a new sleeping bag and are already really equipped good enough.
