Spiderwire is no longer Spectra thread.  It may be as good as it was, but who knows.  In addition, they now market a line of monofiliment that is useless for model flying.

Spectra is a brand of fiber, as opposed to brand of fishing line.  Several fishing lines use Spectra fiber and it will be called out on the box.  Just look for the Spectra logo somewhere on the box to get the "good stuff".  Regarding strength, I have never seen a Spectra line small enough to not have sufficient strength for 1/2A models.  I always use the smallest I can find.

Be sure to get the woven, round stuff, as some brands are flat, and will do strange stuff in the air.   

According to Spiderwire's website, several of their braids are 'Dyneema' which is molecularly the same compound as 'Spectra'  - both are "UHMWP" microfibres and both come in braided (not the 'fused') style which the new rules require.  Spiderwire Stealth braid comes in green and yellow.  We have used the 20 lb. test for 1/2A's with no problems. 

          Mike, I've been using the stealth braid pictured on the left. I'm using the moss green as well, this is mainly due to the only color that was available. This is extremely if not impossible to see in the grass. My son and I use it for 1/2 a combat. I just recently started using it and it holds up quite well. Its been through mid airs and line tangles and shows no sign of degrading. I believe were using the 30lb /8lb diameter. It does get a bit confusing figuring out which one is correct. I Googled Polomar knot and figured out how to tie the knot which is simple. The problem I had was trying to tie two lines the same length that was harder than the knot itself. Ken

Take a look at my Spectra line discussion in the Rules section for the best Spectra line end solution I have found.

Which fish line to use?  That's a really good question.

I went to Gander Mountain a few weeks ago to buy some fish line for binding & reinforcement.  They didn't have what I needed.  When I what I needed, the kid said, "wow, that's reaaaly old.  We haven't had that in a looong time."  I had bought my last roll in 2008.

According to some people who dabble in actual fishing, planned obsolescence is the name of the game in fish line.  They change products a lot faster than AMA changes rules.  But 7-strand stainless steel corecable is a reliable engineering product.