I have not heard of them either. Maybe I don't have that brand in my neck of the woods :o All you can do is try them. I also use polyfil as it stays soft and doesn't bunch in time. I have tried some other brands long ago and they bunched up so badly it looked and felt like my baby was stuffed with meatballs! Not good!
For what it's worth... I have seen references to "Tenderflex" as a material inserted into newborn doll bodies along with beads/pellets/polyfill, but cannot ever remember seeing one that was made in the USA.
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Linda Dreyer~ Forum Moderator Secrist Certified Newborning Teacher & Dealer Apple Valley DW Dealer Play Days Dolls & Collectibles PlayDaysDolls.com (Current Avatar: Erinfrom Secrist Dolls)
Never heard of tenderflex either but I know unicurl is used instead of polyfil. It is small loose curls and is very soft. It feels like feathers (but is not feathers) and works wonderful to fill the babies. You get it in the same type of bag as polyfil.