I am not sure, but I think it is a knit fabric that is knitted in a tubular fabric. I remember seeing some at a flea market, anyway, it is just what it says.. a tube..I think regular knit fabric would work. Hope this helps.
Sure...not sure why I didn't in the first place... Well, here is a link, anyhow! Advance 4575. As you can see, it's very simple. I'm just curious as to what in the world tubing is! LOL The back of the pattern is visible, too.
It's almost a patternless pattern, if that makes sense. There's a tissue sheet (with those perforations, LOL), but it's pretty easy. Mostly I liked the cover. ;)
You can find tubular wool and cotton knits in stores, for T-shirts, skirts etc. (produced in circular manner like a tube, as opposed to fabric with selvedge). Tubular fabrics are cheaper to produce and the advantage is that you don't need side seams. But often these fabrics are not the best quality and they may twist after several washings, distorting the fit.
Check pattern pieces to be on the safe side. It is pretty easy to make this design I think - you have only shoulder seams, if I am not mistaken - good for a quick project or a good quality tubular knit. But if you have some experience sewing with knits, I would recommend going for a regular fabric (=with selvedge).