I used this brush and got good results but I was wondering if there is even better. Are there brushes that are made specifically for polyurethane?
any natural bristle brush will give good results. Stay away from synthetic-type brushes. I've learned to adhere to the old adage: "you get what you pay for" which is especially true for paint brushes. Of course there will always be jobs were the cheap China bristle brushes are adequate. But for above adequate results, the cost of a $10-12 (or more!) that has a wooden handle, brass nailed (not stapled) ferrule and tapered bristles, may seem uncalled for, but produce the best results. The cheap brushes are always leaving behind loose hair strands that are annoying to pick-out (or sand out when dried). The premium higher priced brushes have different bristle ends. These bristles have a "flagged" end cut as opposed to a "square" end cut (think split end). These flagged bristles hold more liquid, leave fewer brush lines and clean-up better. The only caveat is they require regular maintenance (as in cleaning, drying, primping and fluffing) when you are through using them.
Back in the day, it was natural bristle for oil finishes, nylon bristle for water based. Polyester bristle came along touting good for any paint, oil or water based.
Just as a mention, the foam brushes do a very nice job of laying on a finish, but I would only use them for small jobs, the core wears through the foam under long time use. I do not use them by choice, but I have used them here and there over the years and they are my second choice.
In my experience nylon is crap for oil based paints. A good grade, mid priced brush is what I use on water based paints when finish is important. Here I will not hesitate to used a mid priced polyester brush too.
I use a mid priced natural bristle or polyester brush for my finer work, and the results I have seen under close scrutiny with a bright light looks smooth and free of brush marks.
since thats a garbage dollar store chinese disposable brush, putting it on with a rag will do a better job. no - really. a smooth, low nap rag with no lint or straggling threads will do a better job. quality urethane foam brushes do a nice job too, but if you want a brush of any kind, just remember the finer the bristle, the smoother the finish.
I concur with the lambs wool, the brush and the foam pad. Area to cover sometimes dictates the method of application... Small, the brush, Moderately larger the foam and foam brushes, Large (floors) lambs wool on a broom style handle.
Should small bubbles come, keep an eye on them, they usually disappear after a modest amount of time. Remember that multiple coats are desirable and if some impurities like dust or hair get in your application, don't fret it as long as they are kind of neutral in color, as a slight sanding in between coats is always encouraged, then wiped before the final coats are applied. It is the finish coat you really need to worry about most. All coats leading up to the final are important but you needn't fret over too much.
Temperature, humidity and moisture all play a role in the process and can or cannot impact your experiences depending on what is present in your application time period.
Enjoy the process.