Our Guide to Sleeping Bag Liners

Our mission is to get people outdoors. Since most people aren't enthusiasts who venture outside regularly, you can buy or rent sleeping bag liners. Specifically, about our sleeping bag liner rentals:

We rent sleeping bag liners that are higher end than those rented elsewhere, but still offer competitive pricing
We offer a rent-to-buy program so you don't have to worry about losing money from renting
Our self-service allows you to hire sleeping bag liners whenever is convenient for you

Core function: There's not a core function for sleeping bag liners. You can think of them as sheets, a very multi-purpose piece of bedding! Commonly, these are used: 1) for warmth - either in addition to the sleeping bag or as a standalone blanket, or 2) for hygiene (a barrier between you and the sleeping bag, like how in the hotel the sheet is a barrier between you and the duvet).

Insulation is not about having a heater that's actively blasting hot air at you, insulation just slows the rate at which you lose body heat, by trapping it. This is why the same jacket on one person can feel too warm, and on someone else, can feel not warm enough. Every body works differently in generating body heat, no one else can tell you what will be warm enough. So how do you know? Mostly through the trial & error that comes with experience. This is why renting can be helpful!

Insulation counters 3 of 4 ways that we lose body heat

	How your body loses heat (high level physics)	How to counter this
Evaporation	When your body's temperature rises, you sweat. That sweat evaporates using your body heat, so effectively taking it away, allowing you to cool off	Unfortunately we can't not sweat, instead we want to remove sweat quickly & not allow it to evaporate off our skin. This is not typically thought of as 'insulation', and it's reviewed in the sub-section on Base Layers in our clothing guide
Conduction	Your body loses heat through direct contact with solid matter	Clothes or gear creates barrier(s) of dead air that slow the rate of heat loss (detailed how it works below). Barrier(s) needs to: Trap the right amount of dead air: you don't want to freeze or overheat, which is why clothing & gear come with different quantities of insulation to trap different amounts of dead air. This is also why layering works, each layer traps a little bit more! Be a good fit (generally form-fit): a small heater may never heat up a large room. In that same way, if clothing or gear is sized too large, your body may not be able to warm up the excess dead air to equilibrium, and so you may continue to feel cold
Convection	Your body loses heat through direct contact with circulating liquid or gaseous matter This is actually a variant of conduction. Liquid or gas next to you is warmed by conduction, but then that liquid or gas moves away (since it's circulating), and is replaced by colder liquid or gas that gets warmed again, and so on.
Radiation	Your body loses heat just because it's warm This is how the sun heats the earth through space, via infrared rays	Use a material to reflect heat back, like a mirror! Emergency blankets & the insides of some jackets use Mylar to do this (it's that shiny, metallic stuff you also find in many food wrappers). Why don't we just have Mylar jackets & sleeping bags (which would be so much less expensive)? Because it's not very durable & can be too crinkly or crunchy for regular use

How does a barrier of dead air work?

Without a barrier our bodies lose heat to the environment: there's air flowing all around us (convective heat loss) & we're almost always touching something, even if it's just our feet walking on the ground (conductive heat loss). With a barrier (whether it's clothes, shoes, anything), instead, we lose heat to the barrier, and then the barrier loses heat to the environment. Ideally, the rate at which we lose heat to the barrier is roughly equal to the rate at which the barrier loses heat to the environment; this enables equilibrium, where we feel comfortable. For example: when you put on a jacket, it initially feels cold, until we've lost enough heat to it (warmed it up), then we feel comfortable. If these rates aren't equal, then discomfort can happen. For example:

When you exercise rigorously, you can feel too hot. What's happening is that your rate of body heat loss is really high, higher than the rate at which clothing can dissipate that heat
When you put on a really thick jacket, you can feel too hot. What's happening is that the jacket thickness reduces the rate of heat loss to the environment compared to the rate at which we lose heat to the jacket, allowing us to overheat it
When you put on a really thin jacket, you can feel cold. The opposite is happening, the rate of heat loss to the environment is greater than our ability to heat up the jacket, so equilibrium is never reached & we never feel warm

The most effective barrier isn't any material, it's actually dead air (aka dead space or dead air space). This is air that is trapped & not circulating (because if it were circulating, then that implies a hole in the barrier, in which case you'd lose heat by convection; this is why unzipping helps you cool off & why most outdoor clothing or gear has cinches or velcro at the openings). For example: a thick down jacket is warm not because there's lots of down feathers, but because an inherent property of down is that the feathers are very puffy--they expand & take up lots of volume (this is called lofting*). In the voluminous space that the down feathers take up, there is a lot of dead air that can be trapped! The voluminous space is also why it looks so thick, when in fact, it's not about thickness. The less dense & more voluminous a material, the better it insulates by trapping more dead air. For example, a 'thick' sweater is woven in a way that it traps lots of air pockets, compared to a regular shirt.

By that same rationale, a barrier can lose its insulation power if it's compacted or compressed in a way where it can't trap as much dead air. This is why:

For sleeping bags you want a sleeping pad below you, since below you, the bag is compressed & doesn't insulate as effectively from the ground (which is a significant source of heat loss through conduction)
For clothing there are insulation technologies (see the sub-section on Middle Layers in our clothing guide) that don't depend on lofting, since sometimes clothes need to be tighter fit
For storage & maintenance it's important to only compress insulation when you need to (e.g., you're in-transit) & not for long periods of time (at home in storage). Specifically if a lofting material has been too compressed, you may proactively beat it out to get it to work

*Fill power is a measure of how much a material can loft. The higher the number, the more volume it expands to take up, and the better insulation

Do you really need it?

No. If you're borrowing someone else's sleeping bag (rather than renting a sleeping bag from a rental shop where certain cleaning & sterilization practices have to be followed), you may find it easier to rent a sleeping bag liner for hygiene purposes .

For more info, read our 'what you really need' protip

What we carry

Material	Synthetic	Cotton
Material	Mummy-shaped	Rectangular-shaped; fully opens, best if more space is needed
Model
Model	Cocoon Microfiber liner	Cocoon Cotton liner
Buy MSRP with tax	$27 value	$33 value
Rent	$5+
Weight	9oz 255g	15oz 425g
Carry size & notes	A regular burrito	A super burrito

General Notes

We choose what we carry based on extensive research on what's the best value to our customers (e.g., price given performance & durability features) across all the top brands. We specifically do not carry every brand & model; for details on why we do/don't carry certain items in the following What To Use & How To Choose section
Buy prices a grayed out box indicates we don't sell it (we may only rent sleeping bag liners of this model)
Rent prices are the starting prices; enter trip dates on our Catalog to get exact prices (based on total trip length, not per day!). We also don't charge sales tax, an automatic savings of almost 10%!

When you hire sleeping bag liners online, you can select from available options or we'll pick out something for you. You can also write-in any preferences on the last page of checkout. This section describes the majority of our models & options, but sometimes we carry others.

What to use & how to choose

Sometimes it's easy to get lost in all the hype of something new (over-spending often happens on features). Our guide focuses on the fundamental factors you should always keep in mind (thus, this short list is similar across all items). Then only at the end do we have some questions to get you thinking about other minor features. Also take advantage of renting sleeping bag liners to try out what works for you!

We highly recommend reviewing Type or Style first, where we review what you can use to address the Core function--a regular item you have at home may work! The other factors are secondary & depend strongly on the Type or Style you've picked; in fact, for other factors data charts are generally only for a specific Type or Style that we carry (e.g., as a gear shop, would be outdoor-specific products).

We've organized the most commonly used items people use to address the Core function below, with example images, characteristics, features, etc.

With sleeping bag liners, like with sleeping bags, there are 2 primary dimensions that you should consider in terms of type or style.

Name		Sheet	Sleeping bag liner*
Name		Single sheet, thinner than a blanket	Think of a sheet folded in half & stitched together, may also have a hood
Example images
Effect on other factors	Price	$10-50	$10-60
	Warmth Given shape-only	No comparable temperature rating Not enclosed, so doesn't keep out drafts & may create excessive dead air	Adds up to 8F (4.4C) Enclosed & may be form-fit to minimize drafts & excessive dead air
	Size (Capacity)	Twin to king size	Individual sized
	Weight	Not optimized for weight	Up to 16oz (454g)
Why we do/don't carry it = we rent = we sell		Not specific enough for outdoor use	Standard for most outdoor uses

*Sleeping bag liners also come in rectangular or mummy shape. Since this shape impacts other factors similarly as we've already discussed for sleeping bags, and the shape is less of a big deal since the liner is more of an accessory item, we have not separated liners into shapes here.

Like a sleeping bag, there are larger liners for larger people. Since liners are already so small & lightweight, we won't do an in-depth analysis here, but the same concepts apply as from sleeping bags: the larger the liner, the more expensive & heavy. And with larger liners, there's a trade-off between roominess & insulation.

Most people are not super picky about material, but it is important to call out because this will affect other factors, most importantly, price.

Sleeping bag liner material		Silk	Synthetic (e.g., microfiber)	Cotton
Effect on other factors	Price	$40-60	$20-40	$10-30
	Warmth*	Up to 8F (4.4C)	Up to 6F (3.3C)	Up to 4F (2.2C)
	Weight & Size (Compactness)	Up to 6oz (170g)	Up to 10oz (283g)	Up to 16oz (454g)
Why we do/don't carry it = we rent = we sell		Much more expensive relative to the improvements in weight savings or warmth	Versatile for most outdoor uses, therefore more worth the money	For rent for sleepers who need extra capacity; extremely limited availability, please write-in a special request when you reserve
Why we do/don't carry it = we rent = we sell			We only offer liners for rent since most people would just buy a sleeping bag (whereas with rentals, even though bags are sanitized between uses, some people want a hygiene barrier)

*Warmth added when paired with a sleeping bag. Whether the max is attained really depends on individuals, your body heat generation, other layers, etc.

Here, we give you a list of questions to start thinking about other features. We hope our approach of savings these features for last gets you to more critically think about what you need & not get caught up in the hype of what's cool and over-spend your budget. Remember, we allow you to hire a sleeping bag liner so feel free to try out various models with different features.

Is it completely stitched shut or does it use buttons or velcro so that you can undo it (similar to unzipping a sleeping bag)?
Is there a way to cinch it tight around you?
Does it have a hood?

Usage tips

It's easiest to get into your liner first, and then get into your bag!

Maintenance tips

Cleaning

This can be washed in a regular washing machine, like doing sheets

Repairing

Sew up rips, tears, or holes, or apply a patch; generally any tailor should be able to do this

Storing

Store when clean & dry. Since this is basically just a sheet, it's less imperative to store it loosely, as it is with other gear

We have a general protip on how to store & maintain gear that we highly recommend reviewing as well. If you send us video or a good photo series, we may be able to help you evaluate your repair needs.

The exact numbers (e.g., weights, dimensions, prices, etc.) used were updated as of September 2019 .

SUN		MON	TUE	WED	THU	FRI	SAT

	UNSTAFFED 24/7 WHENEVER RENT only Unlock gate & door via smartphone self-service Yes you can rent at the door! Limited selection of gear (what's in our lockers); extra sizes for clothing where possible





		STAFFED 3-6pm WEEKDAYS BUY, RENT, or BORROW No smartphone required Full selection of gear to try & test (including all rental gear, so you can check condition yourself!) Exceptions to standard Staffed hours (e.g., holidays) in the upcoming 14 days: None in the next 14 days

Our storefront

Directions

Our Guide to Sleeping Bag Liners

What we carry

General Notes

What to use & how to choose

Usage tips