Poplar vs Red Oak

[pierhogunn]

Which is stronger
Which is more stable ( resists swelling when it gets damp / wet) than the other one

[cabinetman]

Which is stronger
Which is more stable ( resists swelling when it gets damp / wet) than the other one

Each of them have their advantages and disadvantages, but IMO, Red Oak is stronger. To pick one for their resistance to moisture would depend on their application. I can't think of a situation where I had to make that consideration. I also can't think of a consideration where one would be used or the other for the same project.

Poplar is a stable wood used quite a bit for fabricating furniture structures for upholstered pieces. It's fairly inexpensive.
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[dkerfoot]

Neither are very good for wet/damp conditions. Neither would normally be used outdoors unpainted.

White Oak has some good qualities for wet conditions, but requires an appropriate finish to avoid discoloration.

Describe the actual project you are considering and we can provide better feedback.

[pierhogunn]

I am using 3/4" dowels for the joints in some aluminum flag poles, and this weekend I discovered an issue with moisture and the joints in my prototypes, the poplar swells inside the aluminum tube and becomes very difficult to remove

[cabinetman]

I am using 3/4" dowels for the joints in some aluminum flag poles, and this weekend I discovered an issue with moisture and the joints in my prototypes, the poplar swells inside the aluminum tube and becomes very difficult to remove

Why not use a plastic type dowel like this?
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[Uncle Cracker]

Another option would be a smaller diameter aluminum tube.

[LCHIEN]

I consider the standout property of red oak is that it has a very open grain, so open you can see through a thin slice crosscut... like maybe 1/16th inch which would be more or less completely opaque with other woods. Wikipedia says this about the open grain:
"Red oak wood grain is so open that smoke can be blown through it from end-grain to end-grain on a flatsawn board"

while its an attractive hardwood, any application where you might want to block water or air with the wood should take this into account.

Poplar OTOH is also a easy to work hardwood, but its appearance is so-so and its hard to finish. Which explains why its much cheaper than other hardwoods. Poplar is suited for projects where nicer wood is called for but which will be painted.

I would imagine Red oak would soak up water like crazy if the end grain was left exposed... would probably cause the whole wood to swell, but i'm not sure about that.

Ha, here's another comment seen on the web:
Question: How many root beer barrels could you make from a red oak tree? Answer: None - red oak has big pores, so all the root beer would leak out.

[rja]

Be careful of red oak/iron contact. The tannin in the oak contains tannic acid which will rapidly corrode the iron and stain the oak black.

[pierhogunn]

if the red oak is so open, could I force some poly or some thinned out epoxy into it to stabilize it? ( I have a hand operated vacuum and could build something to draw the epoxy up through the dowel like it was a straw