Center zip vs L/R side zip

If the center zipper is on bottom (beneath your body), then I can see an advantage that it wouldn’t require a draft tube, resulting in small cost and weight saving.

But if it’s on top (I’m not familiar with such a sleeping bag), then I’d see this as a disavantage compared to a side zip back: it doesn’t seem a draft tube would be effective in this arrangement.

Though I suppose then, yes, that could be convenient to get in and out of the bag, if the weather is warm enough that a draft tube isn’t important.

There have been some center zip , at the top, bags.*

Some liked them but obviously not not enough did to make the design more popular.

My impression would be that if you had a zip at the bottom without a draft tube the zip would feel uncomfortable on your back  (or side…)

*Probably the best known was the GoLite Adrenaline, but Eureka,Nemo,Sierra Designs, Valandre all made at least one.

Well, one advantage is (we have one such a bag with a center top zip) that it allows you to strip down the bag below your arms (while the rest of your body stays in the bag) so that you can e.g. eat while you sit straight.

I have a valandré “la fayette”.

I like the step in and out but not the velcro they use for making a kind of draft tube (a big problem when wearing clothes.)   I is easier to prevent drafts with a zip and draft tube along the side.

I liked the central entry so much that i made a winter sleeping bag with two zippers for holding the insulation layer

Thanks for the input everybody. Seems like interesting. But not in the market immediately to get  a new one. So it does appear it offers some advantages, but not necessarily a must buy option in how a bag has been designed.

I used to own a Golite Adrenaline. I found venting really hard with the center zip. Opening the zip would result in uncovering my upper body almost completely (too cold) while leaving the bag zipped up was too warm. With a side zip, opening the zip only creates a small opening for heat exchange, enabling controlled venting.

I’m primarily a tossing side sleeper and so I prefer a center zip, as I often change positions through the night from belly up to either side.

A disadvantage would be the inability to zip two bags together.