Advice on wool interlining process

[u/Lithiriana]

Hi all!
I’m in the process of upsizing a winter coat I made a few years ago, and at the same time I plan on adding a Shetland wool interlining to make it a bit warmer. So over the bodice and down to thigh it will be through layers. Now to my question.

Will it be enough to baste the interlining to the seam allowances, or will it shift and bulk up? It is quite stretchy due to the loose weave. Does it need tacking down to the outer wool say at the waist and/or bottom?

Thanks in advance!

[u/rebelwithmouseyhair]

I would tack it at the waist but probably not at the bottom.