And there is an elastic draw string around the hood of the jungle bag that degrades in a couple of years and afterwards it doesn't work properly anymore. Of course its sewn in.
If you wash in foreign standard washing machines where you can't control the spin dry speed the thread will pull out the fabric. The temperature recommendation of all sleeping bags assumes that you wear thermal base layers in your sleeping bag, yes, they have to assume that you wear winter underwear in your summer sleeping bag in order to keep the bags comparable under each other. That means, that the jungle bag is indeed meant for real jungle. Or Mediterranean high summer conditions.
The Snugpak Special Forces 1 is made in Britain according to military specifications, fits perfectly with the Snugpak Special Forces bivvy bag and both together into the issued British army summer sleeping bag compression bag or a 8 litres Snugpak drybag or a 7 Litres Ortlieb PS10 dry bag.
I used the combination really often, surely 1000 nights or more, and highly recommend it.
The Snugpak Jungle Bag is a disposable Asian made low budget offer. You have to pay attention where the Snugpak equipment is made. If it's Asian made, it's for entry level recreational use, if it's UK made it's the best of the best you can get, constructed for professional use, and regarding the still pretty low prices the far better deal than their imported stuff.
The Snugpak Special Forces 1 has a central zipper and no moskito net. It's part of the Special Forces Sleep System that stands in competition with the Carinthia offers.
The superior jungle bag is the Carinthia Tropen though, that's issued in the German army. It has an inbuilt mosquito net and the temperature recommendation fits like the Snugpak SF1 to middle European summer temperatures. 5°C in winter underwear means approximately 10°C in shorts and t-shirt, and that's what you surely need for summer hikes in Britain.
Once I did wear in the Snugpak Jungle Bag polycotton shorts, breefs, t-shirt, short sleeved shirt and light fleece jacket with thin socks and had a pretty cold night in Bergerac, next to Bordeaux in the end of July! Unfortunately I hadn't much more with me.
I used the Snugpak SF1 this whet and cold July in Brittany and it was fine like last year over there, where we had much higher temperatures. Without clothing I can use it well in south France during the summer, but also with the clothing of the day apart from waterproofs worn in it, it serves me down to the freezing point, I suggest to be a bit careful in that case and assume rather 5°C as the limit if you aren't used to be outdoors all year round and not very experienced. There are some winter camping tricks to learn if you want.
In your case, because you already own the Defence 4 I rather suggest to have a look at the Tropen and a used German Army bivvy bag, if you don't want to buy a new one from Carinthia. The Dutch M90 bivvy bag or issued British army bivvy bag should work fine as well, but the German one is better constructed than the old Dutch one and more comfortable to enter than the much cheaper but also very good British one.
Youngsters can get the British one, grandpas are better served with the German one due to its central zipper. Such a Goretex bivvy bag has a pretty long life time, by the way. If you are already 40 years old think about the German one!
If it gets really cold you can put the Tropen into the Defence 4 and both into such a large military bivvy bag and you will sleep like in a heated room, also on snow.
It's hard to tell if the Snugpak SF system or Carinthia Tropen + Defence 4 is the better option. They are very similar but have different constructions for a different use in similar temperatures.
Of course you can also combine the Snugpak SF1 with the Defence 4. But I am unsure if the Snugpak SF bivvy bag will fit correctly over the Defence 4 if there is an outgrown man in padded army suit and the Tropen inside.
I think I would stick with the Carinthia system if I would have already the Defence 4. The most important difference is the mosquito net in the Tropen construction. It's up to you to decide if just an additional head net would serve you as well. In my case it does, but we don't have so many midges in most parts of Germany most of the year.
