Why are there so few sleeping bags with centre zips? Short or long?

when you say center zip, you mean a zipper along the top of the bag, right down the middle?

I make my own and prefer the center zip.  I like it because when unzipped, the two sides can be sort of folded under a bit.  Stays out of the dirt.  And there is sort of a barrier on both sides that keeps dirt from being knocked into the sleeping bag.

On the other hand, maybe the zipper is where air leaks in the most, maybe worse to have that on the top.

Maybe bags have a side zip just because that’s how people make bags.  Tradition.  It’s gone viral.

As Jerry mentioned, I think these have become passe because the zipper is a spot where insulation breaks down (heat leak).  Having the zipper up makes this worse.

Enlightened Equipment have two sleeping bags with center zipper, but the zipper faces down:

https://enlightenedequipment.com/sleeping-bags/

Last I checked they were more competitively priced than Nunatek.

I never had a problem with a cold spot on my Egge expedition sleeping bag or my old Egg military bag. Before that my old cotton shelled bags also had the short zipper right in the middle

Centre zipper is so simple to operate and if you are a climber it is also the easiest place to tie into if you add a second slider

The EE have full length zippers, a total waste of mass in my experience where the less is more and least zipper is better.When I say long zipper I really meant 40 inches or so Short for me would be 24 to 30 inches

If I could sew UL fabrics I might have a go at making my own but my machine is set-up for canvas and other HD stuff and will not sew modern UL fabrics

I’ve been making pulk and sled hauling harnesses

Sierra Designs has a range of zipperless bags.

I liked the idea but they haven’t set the sleeping bag world on fire.

https://sierradesigns.com/zipperless-sleeping-bags/

”Enlightened Equipment have two sleeping bags with center zipper, but the zipper faces down:”

Why does the zipper have to be on the bottom?  Just rotate the bag 180 deg. Of course, if there is no draft tube then there is the possibility of heat leakage.

The EE bags are designed so you can have the zip top centre, side or under as you like.

Simply too much zipper and therefore unnecessary extra weight with that style of quilt

EE has the custom option with a 3/4 zip.

Simple reason for things like this being not available, no demand. Anything is possible custom.

Yes Franco but those are quilts not sleeping bags. Small but important differences are the lack of a hood and insulated zipper guards

Ken maybe that is because not enough newcomers to overnite cool and cold weather walking have had the opportunity to try them. Naturally enough they are not as versatile as a bag with a full zip but when you want maximum warmth with minimum weight full zip sleeping bags lose out.

I have googled some really nice Chinese sleeping bags with short centre zips, the problem being that the Chinese do not make gear for XXL Tall western bodies

North Face makes them. I’ve never tried one, but I’ve seen the listings.

All the Patagonia sleeping bags have center zips:
https://www.patagonia.com/shop/luggage-sleeping-bags

And their Hybrid bags are insulated just from the waist down, so a kind of half-bag with an upper shell:
https://www.patagonia.com/product/hybrid-sleeping-bag-regular/70070.html

In the 1960s some people (cough) started backpacking in old US Army cotton-and-feather sleeping bags with a top zipper. Cold air leaked through that zipper very easily. Then new-fangled nylon-and-down sleeping bags came along with a side zip and draft tube that kept the cold out and seemed like a miraculous invention.

Have rarely seen top-zipper bags since then. Was quite surprised when Patagonia revived the design.

— Rex

Zpacks Classic 3/4 zip sleeping bag. Can be used as a quilt early in the evening or on hotter nights. Zip it up and cinch it down as it gets colder. Zipper above or below me with this bag has never really been noticeable until it gets down to the low 20’s. Just depends on the temperature of how I’ll flip it

That new Patagonia is a revival of the old Chouinard UltraLite but having tried one I don’t think they got it right on the sizing It is quite narrow, the half bag with windshell needs a cowl to perform as a climbers bag but it is a step backwards in the right direction. I forgot about TNF’s range but the coolest bag isn’t brought into the country and they won’t sell to an overseas address even with a US credit card. A real PITA

My girls were doing Outdoor Ed and they got Chouinard UltraLites just after the kerfuffle and the sell-off to become Black Diamond and I got a bargain with them.

There was the Mountain Hardwear Lamina but it is discontinued

“Simple reason for things like this being not available, no demand.”

like I said, maybe it’s just tradition.  Zippers are put on the side.  I like it though probably not that big a deal.

I have had it cold where the zipper is.  When I let the down shift to the sides.  You have to fluff up the down occasionally and get it evenly distributed.  But the same thing can happen with a side zipper, down shifts from the top down to the sides.  Maybe a little worse with a center zipper because it’s the end of the baffles.  If it’s cold, I wear an insulated layer underneath so it all averages out anyway.

Several hundred BPL members attending the GGGs, never saw one center zip. Still have never seen one outside.

Does Edward ever dream of warm weather trips?

My Eddie Bauer Bag from 1970 has a top center partial zip.

My feet sometimes get way too hot and there is no way to vent/cool them.

The Nunatak bags are center zip.  I know they are known best for their quilts, but do sell well respected bags.  I’m pretty sure they would customize just about anything you want.

https://nunatakusa.com/sleeping-bags/186-alpinist-ul.html#/

I’ve been on a couple trips with you Ken including a GGG, next time I’ll have to show you my center zip : )

Warm weather trips you don’t need a sleeping bag. For summer I use a silk sheet or my old army tropical blanket, for cool weather I use my Nunatak synthetic overquilt. Sleeping bags are for when it is cold.

Thanks Jerry, I’ll take your word on it, lol.

Not that there is anything wrong with that.

Another quilt/bag hybrid is the Feathered Friends Flicker.

Outdoor Gear Lab’s current Editor’s Choice.

Stellar review from Section Hiker:

https://sectionhiker.com/feathered-friends-flicker-40-ul-quilt-sleeping-bag/

Takes an interesting approach to the design of the zip baffle:

If the zipper is on the side, gravity helps keep the flap in place covering the zipper, as long as the flap is attached to the top half of the bag.

Also, and this was a big selling point when side zippers on mummy bags became all the rage, side zips allow you to join two mummies together for a double bag. Doesn’t work too well with center zips.