Picking the Right Gear: Sleep Systems
- West
- Sep 18
- 6 min read
If boots are the foundation of your performance during the day, your sleep system is what determines how ready you’ll be for the next one. Milsim events can last anywhere from a single overnight op to multi-day scenarios. And while pushing through with no rest might sound hardcore, the reality is simple: if you don’t sleep properly, you won’t perform properly.
But here’s the thing: when I talk about sleep systems for milsim, I have my own definition of what a milsim really is. Setting up a trailer or a tent in a fixed location with tables, microwaves, and burger stands doesn’t fit my view of milsim. That doesn’t mean those types of events are bad per se—it’s just that, for me, milsim stands for military simulation. Sharing beers and joking around with players from the opposing team at the same campsite doesn’t simulate any aspect of a “real” military conflict.
What’s most intriguing for me personally about a proper milsim—rather than a big skirmish or sandbox-style event—are all the elements beyond just shooting your gun: tactics, strategy, fieldcraft, and actually taking care of yourself throughout the event. It’s about carefully considering your gear so you can operate at your highest capacity for the entire duration. That’s what gives me the full experience and the chance to really immerse myself in the event.
So, with that in mind we’re not talking about luxurious camping setups. Forget tents, big mattresses, or bulky gear. You need something lightweight, compact, and durable – gear you can pack, carry, deploy, and stow quickly while still keeping you warm, dry, and hidden.
This guide breaks down the three essential components of a milsim sleep system: bivy bags, sleeping pads, and sleeping bags.
Bivy Bags – Your Micro-Shelter
A bivy (short for bivouac) is essentially a minimalist shelter for your sleeping bag. Instead of carrying a tent, you slide your sleeping bag into a bivy cover that protects against the elements. Think of it like a waterproof outer layer for your sleeping bag.
Why a bivy for milsim?
Keeps your profile low – easy to stay concealed.
Faster to deploy than a tent.
Provides an extra layer of weather protection.
Packs down small and light.
What to look for:
Water resistance: A waterproof bivy keeps you dry in rain but may trap condensation inside. Breathable fabrics (like Gore-Tex) reduce this but cost more.
Durability: Military surplus bivy bags (e.g., from the US or British army) are tough, affordable, and reliable.
Zipper placement: Side-entry is easier, top-entry is more weatherproof. Zipper placement and quality also make it more or less easy to get out of the bivy bag quickly if you need to defend your position. A good bivy offers both zipper and button closures—buttons make it easier to get out quickly, but they provide less water resistance. Therefore, you can adjust the closing method depending on the conditions.
A bivy bag can come either with or without tent poles. The ones with poles usually come at a higher price, but they add extra comfort and can also serve as a good option for setting up an observation post.
Pro tip: If you expect heavy rain, pair your bivy with a lightweight tarp overhead. It adds minimal bulk but gives you a huge comfort upgrade. Especially since you can keep your head outside the bivy, which helps prevent condensation from building up inside. This is also a great solution for keeping you gear dry and under cover.
Sleeping Pads – Don’t Skip This
Many new players underestimate the importance of a sleeping pad. But here’s the truth: your pad is not primarily for comfort – it’s for insulation. The ground will suck heat out of you all night long if you sleep directly on it, even in a high-quality sleeping bag.
Types of pads:
Foam pads
Cheap, light, durable, no risk of puncture.
Bulky and less comfortable.
Military-issue roll mats fall in this category.
Foam roll
Self-inflating pads
Balance between comfort and pack size.
Offer better insulation than plain foam.
Can still puncture, but usually more robust than ultralight air mats.
Self-infalting pad
Air pads
Very compact and comfortable.
Insulation depends on whether they have an internal reflective or foam layer.
Susceptible to punctures – always carry a repair kit.
Usually takes a bit more time to deploy.
Air pad from Kilos Gear
Pro tip: Look at the R-value (insulation rating). The higher the R-value, the warmer it is. For spring/summer milsims, R-value 2–3 is usually fine. For colder nights, aim for 4+.
A good way to add extra insulation is to place a space blanket underneath your sleeping pad or mat. It provides a significant boost in warmth compared to the minimal space and weight it adds to your kit.
Sleeping Bags – Your Heat Trap
The sleeping bag is the heart of your sleep system. It doesn’t generate heat – it traps the heat your body produces. That means choosing the right one for the environment is crucial.
Key factors:
Temperature rating: Look at comfort ratings, not extreme survival ratings. If it says “comfort 0°C,” you’ll be fine down to around freezing. Extreme survival usually means you won't die, but you'll be miserable...
Shape: Mummy bags are warmer and lighter; rectangular bags give more room but lose heat faster. This also depends on your “sleep style.” Personally, I never use mummy-style bags because they give me a feeling of entrapment.
Fill material:
Down: Lighter and warmer for its weight, but expensive and loses insulation when wet.
Synthetic: Bulkier and heavier, but cheaper, dries faster, and insulates even when damp.
Weight/pack size: Always balance warmth with portability. For multi-day milsims, lighter and smaller is usually better, as long as it matches expected temperatures.
Pro tip: Military surplus sleeping bags (like the British Army modular system) are affordable and durable, but often heavy. Civilian outdoor brands (like Snugpak or Carinthia) offer lighter, more compact alternatives. When getting into your sleeping bag, try to wear as little clothing as possible. It takes time for heat to build up, and you don’t want to start sweating and end up with a damp bag. The best way to add warmth is to wear a beanie and/or a balaclava to bed. If it’s really cold, or if you want to pre-heat your bag, boiling water and filling canteens or similar containers to place inside the bag will quickly generate heat and keep it warm for hours.
Building Your Sleep System
When combined, these three parts make a modular system you can adapt to conditions:
Sleeping pad – Insulation from the ground.
Sleeping bag – Heat retention.
Bivy bag – Protection from weather and concealment.
For example:
Warm summer op: Thin synthetic bag + foam pad + surplus bivy.
Cold autumn op: High R-value inflatable pad + 3-season bag + Gore-Tex bivy.
Long milsim with changing conditions: Midweight sleeping bag + modular pad + tarp over bivy for flexibility.'
Pro tip: If you’re using a bivy bag, foam roll, and sleeping bag—set them up as you would for sleeping, then roll them together into a single bundle. Store the bundle outside your backpack, and when it’s time to sleep, you can simply unroll it and everything is ready to go.
Scenario | Bivy | Pad | Bag Type |
Lightweight summer / “speed” ops | Something ultralight (e.g. Katabatic or Helium bivy) | Ultralight air pad or combo foam/air with R ~ 2-3 | Lightweight 1-3-season bag, synthetic fill for damp resilience. Carithia jungle |
Cold or mixed weather milsim | More durable, waterproof bivy (maybe MSR Pro or Combat style) | High R-value insulated pad (e.g. NeoAir XLite, Exped SynMat or Kilos gear) | Good 3-season or even 4-season bag, possibly down + water-resistant shell. Carithia defense 4 |
Harsh terrain / long event | Roomy bivy with good weather protection (Helium, Snugpak, Carinthia) | Durable pad; maybe combine foam + inflating pad layers to prevent failure | Carithia defense 4 |
Field Tips for Better Sleep
Change into dry clothes before sleeping – never sleep in sweaty gear.
Ventilate your bivy slightly to reduce condensation.
Use your spare clothes as a pillow or extra insulation.
Keep socks just for sleeping – dry feet = warmer night.
Keep electronic items inside your sleeping bag – batteries and similar gear lose capacity in cold temperatures. Just make sure to store them safely—nobody wants to wake up with their sleep system on fire.
Be ready to fight - Keep necessary combat items within easy reach, and always wear protective gear such as ear and eye protection.
Practice setup at home before your first event.
Final Thoughts
Sleep systems aren’t glamorous. They’re not the first thing people think about when building a loadout. But when the sun sets and you’re trying to get three hours of rest before another day of operations, you’ll realize how critical they are.
A good sleep system doesn’t have to be expensive – it has to be planned, but a good saying that applies to sleep systems is: buy once, cry once. Invest some money into your sleep system. Understand your environment, pick the right combination of bivy, pad, and sleeping bag, and maintain your kit. Do that, and you’ll be rested, alert, and ready to perform while others are dragging their feet.
Slept like a baby in -16° with a carinthia defence 4, snugpak bivy and cheap Ali Air mattress.