1/16" strips of cardstock cut off a large sheet (24") to 1/8" wide with a paper cutter. Exact width is not really critical.
Taper ends down to zero over at least a foot. More is better. Extend beyond the curve if you can, watch out for turnouts. Embed a continuous strip in (a tiny bit of) adhesive caulk under the outer rail when you glue down the track. Works great on 30" - 36" curves. Looks good too. Seems to work OK on 24" too, although I have not yet tried really long trains on the new mountain line.
1/16" is .0625", 2mm is .0787" so that should be OK too for those on the metric system.
Experiment a bit with pins or tiny amounts of glue and see what works best for you. Good luck.
0.125" is too high for HO scale. Since .065 should be just about right. I would suggest using the cord from your Weed Wacker and just slip it under the outer rail of your track. If you have gone through a couple of weed wackers as I have, you probably have an extra spool somewhere around the house.
FWIW I superelevate the roadbed, not the ties. I think it makes it smoother for the track, and easier to ballast. (In the past I’ve always used “ribbonrail” upsom board roadbed, which is fairly stiff. Not sure how this would work with that awful cork stuff.[censored]) I use stripwood, I start with a thinner piece on the straight leading into the curve to kinda ease into it.
Superelevation is a beautiful thing when done in moderation. It should be subtle yet noticeable. I have a 45 degree module with 72" radius curve that is fully eased at both ends. I used 1/16" square balsa stock at the very outside end of the ties, and used a sander to taper the full easements, stopping at the tangent point. It is a beautiful sight when my Empire Builder flows around that curve. jc5729
I used 3/32 superelevation on my 28 inch radius curves without a problem so far… I do spiral in from 32 inch transition radius and transition super-elevation down over 1.5 x my longest car (10 inches or so) for a total transition length of about 16 inches. The only tricky part was going through a curved turnout, that was a bit tricky, but do-able. I used balsa. Given the above conversation, I would probably reccommend 1/16 if >24 inches and maybe 1/32 for < 24inch radius curves. Just my 2 cents.