Alkyd enamel, oil paint, varnish, and polyurethane want natural bristle, which lays them flat; polyester can leave marks in a slow-leveling oil coating — use the white-bristle version of this width class (the 2″ 80352 or 4″ 80354) for oil, or a dedicated varnish brush for clear finishes.
It is not a fine-line tool — the sash and trim brushes cut the lines.
It is not the biggest-field brush — on a whole wall of flush siding or a garage door, the 4″ 80304 covers with fewer strokes.
And it is not a stain applicator: penetrating stain wants the thick, blended body of a stain brush (80202/80203) that floods and works pigment in, not a paint flat that lays a film.
the tip third — a 3″ brush loaded to the heel holds a lot of paint and drips all of it. Lay, spread, tip off: put the paint on, spread it thin and even, then one light pass with the grain to level. Wet edge, always: water-based paint punishes rebrushing a skinned area; work into wet and pull away. Direction: the long way of the board or member. Polyester, in practice: it keeps its backbone in latex where natural bristle would flop, and it shrugs off repeated soap-and-water washing — the whole reason it is the water-based brush. Cleaning: wash latex out warm and soapy while wet, driving the suds into the heel until the rinse runs clear, comb the filaments straight, and dry the brush flat or hung by the handle. Paint allowed to dry in the heel — where the bristle enters the ferrule — splays a brush permanently; a 3″ brush represents enough bristle to be worth that two minutes of care after every session.
Asked before buying
BUYER QUESTIONS, ANSWERED BEFORE YOU ORDER
What size brush should most people own if they own one?
Close to this — 3″ is the width that covers real area while still steering around a panel or a board (§1).
Latex or oil?
Latex and water-based only; the polyester holds its backbone wet. For oil or varnish, use a white-bristle brush (§4, §5).
Why not just use the 4″ for everything?
The 4″ overhangs stiles and 1×4 faces and is heavier to control; three inches keeps the reach the 4″ trades for coverage (§5).
Can I stain a deck with it?
Poorly — it lays a film, it doesn't flood and work pigment in. Use a stain brush (80202/80203) for that (§4).
How do I keep it?
Wash latex out warm and soapy while wet, into the heel, comb, and dry flat — heel care is what makes it a multi-year brush (§3).
