Where I live, I need to keep an eye on temperature and humidity changes. Linen canvas will get very baggy and saggy in the dry wintertime.
A baggy canvas causes the "trampoline effect" - a pronounced elasticity in the center which can drive you nuts when you're painting.
In order to create a stable substrate, I used to put cardboard behind my canvas when I painted. And sometimes it sorta worked.
I even had a 24" stretcher* snap when a linen canvas suddenly tightened up in humid weather. Of course it wrecked the painting. And believe me, re-stretching a painting is no picnic.
The aren't cheap. But if you sell your work, it must be archival. Since I began using Art-Boards, it has solved a thorny long-term problem with those large linen stretched canvases.
The linen is mounted with a reversible archival conservator's adhesive that creates a barrier between the panel and the canvas. This means that a painting can be removed from the canvas panel at any time in the future.
The panels I like have an untempered solid core construction with a solid surface of oil primed #13 Claessens Belgium linen.
This panel is 3/8" thick. It also comes with acrylic primed cotton canvas.
These panels have recessed hanging slots and that makes it easy to hang a wet painting on my studio wall to dry.
They also attach a high quality watercolor paper to their boards.
* Because of that (lightweight) stretcher accident, I only use heavy-duty stretchers for any painting 20" x 24" and larger.