Ttt

For the linen I would use water soluble. Felt does not need stabilizer, so either hoop it alone or use tear away. Hugs. Nan

My advice.... Be sure to wash the felt first. I used felt as a backing for a table runner once. It was a gift for my friend. It looked so pretty when I gave it to her. Something got spilled on it and she washed it. The felt shrunk up incredibly. She tried to iron it flat but it was destroyed. Susan

If this will need laundering do rethink the 'felt' idea. If you use a cut-away for stabilizing, this would also double as an interfacing to make your runner nice and firm.

I have used felt as a batting in table runners, coasters and some wall-hangings.
Be sure to use acrylic felt, though, as wool felt or wool-blend felt is likely to shrink.
My table runners and coasters have been washed many times without mishap. I do the laundry wash in just off-cold water, never warm nor hot. I don't know how the acrylic felt would behave in hot water - I imagine it would crinkle rather badly and lose shape.
AlmaG.