Sorry for the delay in response but I needed to inspect as many black jacket conduits as I could.

All of the ultra-flexible conduits are covered with a black vinyl (PVC) with a vacuum forming process.

Of all of the sleeves I could inspect, the specification numbers were only visable on two. Each had the same numbers and they felt a little "looser" than a third one; a fourth had no number and felt "tight".

My conclusion is that all PVC is the same and the black vinyl jacket will soften with use.

Hope this helps,
Dan