When I heard about polyspan and it was recommended to me, Starline is the brand that I used.

When I used up that roll I bought another batch of polyspan but there was no label to identify what the brand was.  It came on a cardboard roll, unwrapped.  I can't remember for sure where I got it.

I was disappointed in that later batch because I think it was a cheap knock off.  The weave looked uneven with areas that appeared to be thinner.  In some spots it looked like a small hole.  I doubted that I could fill these areas with dope.  It was also harder to determine which was the outside surface and which was inside.  I doubt I will ever take a chance on it.

If I used a polyspan type of material again it will be Thermal Span.  It is identical to polyspan except it is just as strong in the chord-wise direction as the span-wise direction.  The weave looks denser so maybe it takes less dope to fill.  Like polyspan, it has an outer surface and inner surface and is applied the same way, shrinks the same way. 

Thermal Span is available from Harris Design, 5835 Griffith Dr., Brighton, MI  48116.  The price is about the same as what I paid for polyspan.

Yes, buy poly-span from RSM Dist or Stunt Hanger Hobby.   The stuff I got at the local fabric store is a heavier weave and takes more dope.   The next plane will have SLC over the top of it.

Haw.. secret is out...

I still have plenty I got from RSM but also have a quilting wife, who occasionally helps me. I was cutting off the RSM Poly span for a set of wings she asked about it... I gave her a small square and she found ...Yes Jo Ann's and Hancock's of Paducah  a very similar material.

If I even need more, I still think I will get RSM... the 2 yards she got me...yes a bit (OK a lot)  cheaper, is in folded, wide, bolt format with creases...RSM's is on a rolled up tube and easy to lay out and cut with not much waste

To add just a tad to what Mike just said

Close examination of what my wife bought cheap (Jo Ann's)  and the RSM Polyspan:

Jo Ann's version does not (to me) have a distinguishable top or bottom..... I assume the RSM Polyspan has been "fixed" with something like fabric sizing on one face... I asume this sizing significantly heps with how much dope is needed to fill the weave

I made a fairly small open bay test panel and used both fabrics with my typical doping method...
Balsa bare wood Randolf full strength(FS) Nitrate 3 coats, sand, 1 wet coat FS Butyrate, set poly, very thin 70/30 B dope on perimeter.. dry...heat tighten... fill with 50/50 Butyrate fully drying each coat looking of full fill and a smooth feel

The "treated" RSM poly closes with one less coat of Randolph Taunting Dope....to MY eye and finger feel

Once doped, I weighed each and there is not enough difference in my notably small 4"x6" 2 bay trial...extrapolated to a 60 ~70 inch wing the weight gain is probably a game changer

If I did not already have enough RSM Poly for all the models I could possibly build the rest of my life   I would be real tempted to switch to the much cheaper Jo Ann's product

I might even ask my wife to Iron in "Fix Sizing" spray to one side

BUT again the Cost (for me ((not too frugal)) ) is the RSM stuff comes in a form factor that is easy to cut and not waste... I would need to build a LOT of models to consider the meager aggravation of the Jo Ann's Hancock cheaper but nearly the same product

On the Other hand...IF you are a newbie on a severe hobby budget and wanting to built 5~10 models from your youth and do them sort of old skool... the Jo Ann's product WILL work, and be significantly cheaper with a slightly higher aggravation to cut and set

I am not yet ready to show my funky tries at Larry Rengers method
BUT I personally am happy with the result...just have to perfect with MY technique

NOT sure what the hell I am talking about...??

Larry R suggested covering the wing with Poly or silk, or  tissue ---light weight covering and NO  dope......Just final cover with Super Light Covering (SLC) from Phil Cartier...and call it done!...

I now have done two wings this way and it is faster, easier, much lighter BUT my personal technique still leaves visual NOT STUCK down SLC over the Poly....grrrr
BUT in the areas where I don't have issues...really is strong and looks fantastic

BEST advice

Support a modeling friend and get the very good and easy to work Polyspan from RSM...  The Stuff is NOT too much more cost...

BUT, love supporting them as I do... Dharma and the other places have good Silk, so much cheaper, I can not recommend the Brodak, RSM, or other cottage suppliers

Dope ---same advice...I spent first few years returning to this hobby using Sig and Brodak dopes

I Found a REAL aircraft supply in Dallas and bought gallons of thinner and dope..YES ....still pricy, but cost per gallon a LOT cheaper than pints or quarts from our Sig and Brodak friends

I need to address Herman Green's real first question

Yes sir... the Poly fabric can be found with a wide variety of weights and closed or open weaves,,,, just like Silk span

If you suspect you got super light fabric..it is still usable but I highly recommend Larry Renger's method for 36 to 70 inch models...

I suspect for many .15 down to 1/2a models the lightweight poly will be just fine as is

BTW, I experimented and Preval sprayed MinWax H2O (water based Poly crylic) on a Brodak Lil Jumpin Bean I covered with questionable weight Poly off e-bay  ((SEEMED real light and flimsy to me once applied)))... sanded smooth it took color rustoleum fine and so far holding up to my abusive flying