I want some spring in my seat.

[Mikericks]

All, I have an aluminum and fabric Deck chair. The fabric seat has failed. I want to redo the seat with wood slats. 

i want some flex/spring to the seat. 
Does the Wood species Matter much , or is it the thickness that matters ?

no artwork going on here. Looking to make use of that chair frame, and use up some scrap wood. 

[curlyoak]

Quartered Ash. Milling the correct thickness is the key. The species matters.

[Wimayo]

I did this years ago to some aluminum folding chairs probably similar to yours. I used 1/4" thick by about 2" wide cypress slats. I used aluminum pop rivets to fasten the slats to the aluminum tubing. I added some aluminum strap to the chair where there was nothing to fasten the slats to like at the bottom of the back. The slats were then stained. They have held up well for many years. However, as they are folded up when not in use, they are not generally subject to the weather. I think the ash suggestion is a good one, but I'm not convinced the species matters too much as long as the slats are straight grained and free of defects. Sorry. I don't have any pictures.

[Coop]

I have two that stay out 24/7 (shame on me) that have the thread give way and the fabrics is fine. Wife is going to get some nylon thread to see if she can fix them. The sun takes it’s toll. My wife’s uncle has several chairs with the old green and white nylon webbing that must be 25 yo and he takes them inside every night after using them. I need to take lessons.