Oil-based enamels and varnish that must lay off perfectly flat — that finish is the province of soft natural bristle (PREMIER black-bristle 80452-class, Hyde Extra white 47380-class); the synthetic here is for waterborne paint.
The tightest muntins and narrow pockets — where 2-1/2" is too broad to steer, drop to the 1-1/2" 80801.
Huge thirsty exterior fields — for laying a heavy coat over broad rough siding fastest, an oval's larger reservoir beats a flat sash (§5).
And it is not a roller — cutting a whole wall face with any brush is wasted effort.
How the pros run it
01
Pencil grip on the ferrule
for wrist-level control of the line. Load to a third and tap the excess — a cut brush holds its paint in the belly, and a flooded tip drips onto everything below the line. Long, single, unhurried strokes off the long point; let the loaded brush's own weight set the pressure. Come to the line from just behind it, not straight down on it. Cut wet-into-wet with the roller, and only cut as far ahead as the paint will stay open — with fast modern latex that is a shorter run than it used to be, which is why the brush is synthetic. Tip off the tail of each stroke to lift the mark before you reload.
Asked at the counter
BUYER QUESTIONS ANSWERED BEFORE THE CART, NOT AFTER THE RETURN
Is this the "one brush" to own?
For interior wall-and-trim work in latex, yes — the 2-1/2" angular is the most-used width and shape in the trade.
Latex or oil?
Water-based. Oil and varnish want the natural-bristle sibling.
80803 or the 1-1/2" 80801?
This for full-wall cut lines; the 1-1/2" for muntins and tight pockets.
Flat sash or the 2-1/2" oval (80763/80768)?
Flat for a crisp line, oval for maximum paint on long thirsty runs.
