I haven’t yoyoed for a little over a year and I’m finding out that this kitty string is really nice what’s the best kind? I’m kinda confused with there lingo
the normal/ regular polly is a good place to start, it’s nice string, and it works out pretty cheap, I’m not a fan of the Nylon myself, and I haven’t tried 1.5. I find the slim to give me slippy binds once the response pads start to wear, but can be handy in narrower gapped yo-yos. I have some Fat in my case right now but I haven’t tried it yet so I’ll get back to you once I have (or someone else will beat me to it 
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Does the slim not last as long?
haven’t used it enough to make a call on that, but it doesn’t seem to be too different
My favorite is Kitty string Fat, but I also like the regular thickness. I hate anything with nylon in it so I can’t comment on other types.
Never even tried anything from Kitty other than 1.5. It is pretty awesome. Might not last too long, but it is super nice while it lasts. It also has a short break in period.
Note this though: I have only owned YoTricks Bulk String, Expert String, and Kitty String 1.5.
I think its a personal preference so as you go on through your yo-yoing try each out. if you happen to find one you really like stick with it.
Love the fattest poly they make, reminds me of highlights