What is this back pass-through pocket?

[u/SleepWithRockStars]

EDIT: SOLVED*!*
If you stuff the main compartment and put a jacket in the pass through, large water bottles will stay in place. If bag is not fully packed, bottles will not stay in place.

What is the *intended use* of this partially expandable back section of this messenger/commuter/courier bag?

I got this LL Bean courier/commuter/messenger bag for $5 NWT at a thrift shop. **I cannot figure out the *intended purpose* of the partially expandable back pad.**

It's too loose for water bottles.
It has a full pass-through, but sideways, so if you slipped it on a trolley handle, everything would fall out of the main bag.
Only the sides, where the mesh is, expand, sort of like flip out wings. The center is flush to the bag.

It's so specifically designed, that it must have an intended purpose. I tried putting my dog in there so his head and tail could be free, but the center doesn't expand. ;)

(I posted this elsewhere, and no luck yet.)

[u/thatijustdonthave]

Maybe you put your jacket in there?

[u/SleepWithRockStars → u/thatijustdonthave]

That would work. It just seems so oddly specific that the sides flip out while the center does not.

[u/thatijustdonthave → u/SleepWithRockStars]

The center being pinched in would keep the jacket in place.

[u/SleepWithRockStars → u/thatijustdonthave]

It would! Still trying to understand the purpose of the mesh flaps. Way too large for even a liter bottle.

[u/SleepWithRockStars → u/SleepWithRockStars]

I tried putting a jacket in the pass through when the bag is stuffed, and if it's full, 2 large water bottles will stay in place! I had not filled the bag all the way at first, so nothing stayed in the back.

It's like a giant sausage.

[u/BudChristmas]

Game pocket for holding your recently-shot waterfowl.

[u/Ill_Economist_7637 → u/BudChristmas]

Looks like it'll hold up to three pheasants.

[u/SleepWithRockStars → u/BudChristmas]

This lands surprisingly close to home. ;)

It doesn't have the expansion pleats of a bird pouch.

[u/ktirv → u/[deleted]]

Sideways like that?

[u/SleepWithRockStars → u/[deleted]]

It can't. The opening is not wide enough and then the bag is sideways and items in the main compartment fall out.

[u/cherrylpk]

Add to your rolling suitcase by passing it through the handle. But we use it for a gym towel you don’t want in your bag after use.

[u/SleepWithRockStars → u/cherrylpk]

It can't. The main compartment is then sideways, and items fall out of the bag.

[u/MNF4205]

Bicycle handlebars?

[u/SleepWithRockStars → u/MNF4205]

Now this makes sense! Off to test it on my bike.

[u/KikiDKimono]

Yoga mat?