This may be old news but it looks like s-foam is starting to offer parabolic stringers.
And then look under their photo gallery. Their blanks carry the XP designation.
That is very interesting. I just emailed them asking to either give me pricing info or go directly to swaylocks and post it themselves. If they reply to me I’ll post it here. What do you think of the higher density 1/8" PVC stringer that “weighs the same and is stronger than a 3/16 in. bass wood stringer. It is not as stiff as the wood stringer, but only during shaping.” Not sure how that works.
been dealing with these materials in detail…the PVC is more flexy but is also more dense and heavy…so much so I had to scrap using PVC as parabolic stringers…the stringers alone would have added nearly a pound to my finish…for me thats in the wrong direction…a lightweight ply would be better for weight but more difficult to plane and work with…good to have lots of options