The 1.5" size black natural angled Purdy brush is the ONLY brush I use for poly, laquer, linseed oil varnish, shellac. Anything bigger doesn't work well because you will have a hard time controlling build up of applied product in the corners, and overapplying on the edges - causing drips on the bottom side of your piece. Maybe there's a better brush out there - but use it for a decade or so before you come and prove it to me!After several uses the brush will be a bit stiffer, but this is more or less what you want for poly - it will also shed less hairs - SEE NOTE BELOW!!! You need some stiffness to work the thicker poly down so that it flattens properly and gets into the grain of the wood. For the last coat(s), use your newer (but not newest!), more supple brushes with a thinned poly. In my experience the stiffness of the brush overall has little impact on the smoothness of the outcome. Achieving the correct flow of the poly and working at cool temperatures is much more important in achieving a flat, even finish.Clean by working in a small amount of mineral spirits three times (just enough to partially soak the brush), then finish up with two goes of laquer thinner. That last step is essential! Strike the brush smartly on your foot to remove any thinner that wasn't wiped off between each rinse step. Don't complain if you don't clean your brushes right! I'm telling you - 15 years of using these brushes has shown me that they last dozens of cleanings before I worry about demoting them to my "first-coat" brushes.ABOUT THE HAIRS COMING OFF: Pretty much any new brush will do this - this is why I DO NOT like breaking in a new brush! I always break in a new brush on the FIRST coat of a project. By the third coat, and two vigorous cleanings, minimal hair comes off. However, the brush isn't really great until the second or third project. I really hit a new brush on my workbench hard trying to work out any loose hairs before I use it. You want to be real "unkind" to the brush during cleaning, working the thinner in real well with your gloves on, helps to get those loosey-goosey hairs off.They seem to have replaced these with the XL line at my local building supply. Just for fun, I tried one a couple months ago; what a mistake!!! The bristles do not load or release the poly anywhere as effectively as the natural bristles. Absolutely horrible, will never use again!