If you're going camping,
one of these is absolutely essential. You're not going to enjoy your
excursion into the wilds unless you get a decent night's sleep, and
that comes down to ensuring you're comfortably warm. Sleeping bags work
by trapping dead air in the filling to insulate you. Most bags fall
into one of two clear categories:
The fluffy stuff which comes off the breasts of waterfowl is still hard
to beat in terms of insulation for any given weight, although it does
suffer from a drastic loss of performance if you let it get damp, let
alone wet (these days it's possible to improve things by using proofing
agents designed specifically for down made by companies such as Nikwax
and Grangers). Still provides the best recovery from long-term compression,
which is why the Royal Air Force vacuum-pack down bags into their fighter
pilot seatpack survival kits.
To all intents and purposes, polyester fibres absorb no water, which
has to be a big plus for a sleeping bag in a damp environment. Even
when the bag is wet, it loses very little of its insulation value. Cheaper
sleeping bag fillings - usually the unbranded polyester fibre waddings
- have a limited lifetime, further reduced by frequent washing. Polyester
fibre waddings are generally bulkier and heavier than the equivalent
insulation value in down, and their lifespan is much shorter, particularly
if the bag is stored in its stuff sack.
Having said that, many of the top quality polyester fillings come pretty
close in softness, compression and recovery to the performance of down.
Sleeping bags are often quoted as conforming to a particular season
rating - 1, 2, 3, 4, and, oddly perhaps given the number of seasons
in a year, 5, sometimes referred to as expedition. What it's trying
to do is give you an indication of the temperature range the bag is
good for at valley level. So if you planned to do a high-level camp
in Scotland in the spring, what you'd more likely need would be a 4
season bag rather than a 3 season.
spring, summer, early autumn, 0ºC
summer, autumn, -5ºC
summer, autumn, winter, -15ºC
Most manufacturers will quote the suitability
of their bags in terms of minimum temperatures, some even giving the
figures for what's comfortable, and what's tolerable - a distinction
worth bearing in mind. And although they are good indicators, they need
to be balanced against your own metabolism. What's comfortable for one
person may only be bearable for someone else. Neither do such figures
take into account the differences in comfort levels for any given temperature
at different levels of humidity. You'll probably already know whether
you're the kind of person who feels the cold easily, so take that into
account when you make your choice.
Alternatively, stick with a lightweight bag providing minimum insulation,
and simply uprate your bag by wearing extra clothes. Whatever you end
up with, the golden rule is make sure you go to bed warm. Have a hot
drink just before you turn in, or go for a quick jog around the tent
to get the circulation moving.
To an extent, this comes down to the kind of insulation in your bag,
but the amount of space which your sleeping bag commandeers in your
rucksack can have a significant bearing on your total load. One useful
advantage of having two ultra-lightweight bags is that, apart from simply
using one when the weather is kind enough, if you use them doubled up,
you can still pack them separately.
Some amazingly lightweight bags aren't so much lightweight because they've
been made using some new space-age insulation - they've simply been
cut small to use less materials. You don't have to be 6ft 5 and weigh
16 stones for this to be a problem, either, so pay attention to dimensions,
and always take the opportunity to try the bag for size in the shop.
Features To Look For.........
Lightweight densely woven fabrics are the norm, as down and even synthetic
insulation fibres can percolate through even quite close-weave fabrics.
A degree of water repellency is an advantage (stops any condensation
drips from the tent getting too far). Linings vary depending on the
weight and intended use of the sleeping bag. Cotton feels comfortable
next to the skin, but for the same reasons that cotton underwear has
long been abandoned in "performance" situations, it's now
very much relegated to budget bags. Polycotton is a reasonable compromise,
whilst lightweight bags will often use a variation on the shell material
- Pertex is probably one of the most widely used.
The majority of sleeping bags come with full-length zips these days,
and the better ones will have two-way pullers to enable you to ventilate
the bag at the foot without completely undoing it. Bags like this will
usually be available in left and right-hand zips so two bags can be
zipped together (why would you want to do that?). But there are still
some bags which come with short zips, and some without zips at all -
a bit of a struggle to get in, but lighter and more thermally efficient
than their zipped counterparts.
Where bags are zipped, they tend to come with a baffle behind the zip
to prevent cold spots. The effectiveness of these baffles varies enormously,
as does the way they avoid getting snagged in the zip itself. The best
baffles incorporate some kind of anti-snag stiffening.
A useful feature if you're intending to do much cold-weather camping,
as it reduces any bellows effect inside the bag, although it can feel
uncomfortably restrictive to some. Not really necessary for 3 season
Your head radiates heat more quickly than any other part of your body,
so it makes sense to insulate it. At its most basic level, a hood is
simply a flat extension of the underneath of your sleeping bag. The
trouble is, it tends to bunch up horribly when you pull in the drawcord.
Shaped or sculpted hoods do the job much more efficiently.
The standard oblong construction of the cheapest sleeping bag does little
to recognise the fact that human feet stick out rather than lie flat
like Charlie Chaplin's. The majority of sleeping bags use a boxed foot
construction, but there are variations on the theme which do the same
Quality construction counts for a lot. A synthetic bag usually has the
insulation quilted to the shell fabric, and if it's a double layer,
the top layer is stitched to the shell, the lower to the lining, with
the stitch lines offset to prevent cold spots. Some of the more innovative
manufacturers have come up with techniques which reduce the amount of
such stitching, thereby improving the bag's thermal efficiency.
Because down is a loose filling, it's blown into pockets constructed
between the inner and outer shells, the better ones using vertical or
slanting baffles to keep the down in place whilst maintaining the separation
which prevents cold spots.