Protection you stop noticing
The real test of an encasement is that nobody mentions it. If a guest can hear the cover, feel a ridge under the sheet, or sleeps hot because of it, the product has failed even when the barrier works perfectly.
That is why the knit lines are laminated rather than coated, and why the cotton lines carry no membrane at all and rely on weave density instead. Both approaches cost more to make than a coated fabric. Both are quieter.