How to Choose a Sleeping Bag

A sleeping bag is one of the most important pieces of kit you’ll buy. But how do you choose a one that fits your climate, adventure, and comfort? Explorer Julia took the Sea to Summit Spark Pro Down Sleeping Bag to the mountains to find out.

I’ve been camping for yonks, and have spent enough nights practicing mental fortitude while battling the cold to know the value of a good warm sleeping bag. But I’ve never understood the tech of how sleeping bags actually work.

Sure, I’ve had a general inkling – there’s some kind of fill inside, the outer layer traps heat, insulation works its magic, you stay toasty.

And here’s what being toasty looks like

But there’s a lot to consider when choosing the bit of gear that stands between you and a good night’s rest out in nature. Does the type of fill matter? How do you balance weight with warmth? Which features actually make a difference?

I recently studied up on all the things that make for the right sleeping bag, and headed out for a weekend camping trip with my brother. We headed to the Megalong Valley on Gundungurra Country in the Blue Mountains, with the Sea to Summit Spark Pro in tow to test my findings. Here’s how to choose a sleeping bag that suits you and your adventures.

Read more: How To Wash Your Sleeping Bag

What is the Spark Pro best used for?

The Sea to Summit Spark Pro packs a punch as a lightweight but super versatile sleeping bag.

Depending on which comfort rating you choose (it comes in a -9°C and a -1°C) it’s either a 2 season or 3 season bag. Meaning you’ve got options to stay toasty in most temps, although you’re probably not going to want to rely on it in sub -10°C or alpine conditions.

This is a sleeping bag designed for ultralight hiking, with the heaviest temp and size combo clocking in at a measly 861g. This is all without sacrificing any warmth – the frosty night of a mid-winter Blue Mountains trip was no match.

It’s designed with a number of features to keep it flexible across seasons too. We’re talking foot zips, configurable sleeping options (my fave is the customisable armholes, perfect for the sleepers who don’t want the straightjacket experience) and adjustable hood, all to regulate comfort and warmth across conditions.

The armholes are genius

Sleeping Bag Shape

Most sleeping bags will come in one of three shapes – mummy, tapered rectangular, and rectangular.

When sussing what works best for you, there’s a pretty simple rule of thumb when it comes to shape – the less room there is inside the sleeping bag, the warmer it’s gonna be. This is because sleeping bags function by your body heating the air trapped inside.

Mummy sleeping bags are narrow at the feet and fit snugly to the body. These are the warmest sleeping bags with the least amount of extra air inside. As an ultralight sleeping bag, the Spark Pro boasts this shape, as the mummy is often less bulky and smaller to pack down.

Tapered rectangular sleeping bags are also slightly tapered towards the foot, but a little less fitted to the body. The extra room means they don’t pack down quite as small, but they’re a great midpoint if you want to retain warmth and a bit of room to wiggle your tootsies.

Rectangular sleeping bags are what they say on the label – same width at shoulders and feet. These give plenty of space to move around (fab if you’re a restless sleeper) but aren’t quite as efficient at heating and tend to be on the bulkier side. Typically they’re a great choice for warmer climes or car camping.

Sleeping Bag Fill

It’s the perennial debate amongst hikers, car campers, and everyone in between – synthetic or down?

Down sleeping bags, like the Spark Pro, use duck or goose feathers. This kind of fill is king when it comes to warmth, weight, and ability to pack down tiny. The Spark Pro uses RDS-certified down filling so you get a toastier comfort rating without adding on the grams to your pack.

Careful in the rain though – down doesn’t do its best work once wet, and they’re a little trickier to wash.

Down is super warm, but will stay super damp if you get it wet

Always suss the care instructions for a down sleeping bag to get the best lifespan out of your gear.

Synthetic sleeping bags use – you guessed it – synthetic materials for the fill. They don’t pack quite as much of a punch as a down sleeping bag when it comes to warmth, and the fill doesn’t compress to the same degree as down, so they’ll take up a little more space and weight in your pack.

However, synthetic is the winner when it comes to wet weather – they’ll still insulate and keep you warm even when wet, and are typically a lot easier to chuck in the washing machine.

Sleeping Bag Warmth

The temperature rating is probably one of the first things you should check out when looking at a sleeping bag. And there are a few things to consider when choosing the right one.

The rating will typically be showcased across three categories – comfort, limit, and extreme.

Comfort is the temp at which you’ll be able to sleep comfortably in the bag. This is what you want to consider most when weighing your sleeping bag up against the forecast for the best night’s sleep.

Limit is the lowest temp that an average sleeper will be able to keep warm.

And extreme is a survival-only rating, basically the lowest limit that can keep you alive (I don’t recommend choosing your sleeping bag based on this one!).

Then there are seasons, which can help you make sense of what conditions you should be taking the sleeping bag into.

Summer sleeping bags (1 season) sit around +5°C, while 3 season bags are typically the most versatile for year-round use with ratings at -5°C (or even -10°C in some cases). These tend to be a good fit for most Aussie conditions outside of alpine regions.

The Sea to Summit Spark Pro comes in 2 and 3-season options, with your choice of comfort ratings, -1°C and -9°C. I snuggled up in the 3-season version while camping and it definitely kept me toasty as temps dropped below 0.

Still warm even with my arms out and tent open

For true winter sleeping bags you’ll need a 4 or 5 season, with the latter being the most technical of the lot and suitable for freezing conditions.

Of course, these ratings aren’t hyper-accurate and you know your own body best. I recommend adding on a few extra degrees of warmth to your calculations if you tend to run cold.

Sleeping Bag Features

Outside of the main considerations, there’s a whole host of additional features to consider. Some of these might seem small but can make all the difference for the most comfy sleep.

A good hood on a sleeping bag will be adjustable to tighten around your head. This is massive for not losing precious heat through your noggin in the night!

Zips come in all configurations and directions – left-side zips, right-side zips, foot zips, zip guards.

Consider how you might want to tuck yourself in at night (are you left or right-handed?) and how you want to unzip your sleeping bag (do you want to be able to open it up like a quilt?) when choosing one.

The Spark Pro comes equipped with a Free-Flow zipper system, making it one hell of a customisable bag. This includes zips on both the left and right with snap closures that transform the sides into armholes, a separately zippable footbox, and a hood with multiple adjustment toggles. Yes, this means you can wear it like a suit and walk around your campsite in it.

Sleeping Bag Weight and Size

The weight and size of a sleeping bag are a combo of most of these factors – fill, shape, warmth rating, and features all affect the grammage and bulk of a bag.

It’s best to weigh up the climate you’ll be facing against the kind of adventure you’re heading on, and the space you’ve got to fit a sleeping bag into.

If you’re going to be carrying your gear on your back, a tighter shape and opting for down over synthetic will reduce your pack weight. Down-filled, mummy-shaped sleeping bags like the Spark Pro tend to be the smallest and lightest, as down has the best warmth-to-weight ratio.

Synthetic materials and roomier shapes tend to run both heavier and bulkier and are often great fits for car camping, or if you don’t need to carry your gear.

The compression bag helps you squeeeeze the bag down to a packable size

So, what’s the verdict on the Sea to Summit Spark Pro with all this considered? It’s a choice sleeping bag for multi-day or overnight hikes. You’ll get all the pros of keeping your pack weight down, and you’ll get to stay snug and comfy overnight for some valuable Zs.

All in all, choosing a sleeping bag comes down to what works best for you. Match your choice up with your adventures and the conditions you’ll be facing, and you’ll hopefully have a trusty sleeping bag for years of exploring.

Here’s to a good night’s sleep and the energy to adventure onwards the next day.

Na night!

Photos thanks to @aebimedia