Rigid duct, insulated, is always the best option.

Flex duct is commonly used for bathroom exhaust ducts in my mild weather area. Whether or not insulated may depend on the location (cold winters?) and local building code.

Hey Opaone, it seems like they used the same type of duct for both the bathroom and kitchen exhaust. But here is a photo of the attic for the bathroom duct, the other was for the kitchen.

How should I go about this situation?

I was trying to avoid breaking out the brick again from where the duct work vents to the exterior of the house.

Would you recommend using this type of duct

https://www.homedepot.com/p/4-in-x-5-ft-Round-Metal-Duct-Pipe-CP4X60/100196725?MERCH=REC-

Or since this run isn't that long, would this type of duct be sufficient?

https://www.homedepot.com/p/4-in-x-25-ft-Insulated-Flexible-Duct-R6-Silver-Jacket-F6IFD4X300/100396934

Opaone explained it as clear as it can be explained. Now that you know the difference,the choice is yours.

Semi-rigid will work fine in a situation like this. Personally, I wouldn't waste time on insulated, unless this is a cold climate.

Weedmeister, I live in NYC so we definitely do have our cold spells!

Jim,

I posted an answer in your other posting. You have two posting with the same topic. That doesn't work well on this forum.

If you are located in NYC then why is there Romex cable in the attic? I thought the electrical code only allowed BX cable. There may have been a recent change in the electrical code to allow Romex in some applications. You should ask the inspector about this.

I don't see much insulation. How much insulation do you have and what type is it?

No code change in NYC, BX only.