If you want really small travel brushes (that will fit in the small Altoid tin!) Whiskey Painters and Winsor and Newton both make natural hair reversible travel brushes. Both are rounds size 2 – I find the Whiskey Painter brush holds a lot of paint but is very soft. The W& brush doesn’t hold as much but is firm enough to give me a good fine line.
My favorites are my Silver Brush Black Velvet Voyager reversible pocket brushes. They are a blend of squirrel hair and a black synthetic filament. I love these brushes – in addition to some Escoda kolinsky sables I have and some miniature W&N Series 7 brushes, the full size versions of the Black Velvet brushes are the ones I use most frequently indoors. (The travel brushes are the exact same… had I bought the Voyagers initially, I definitely wouldn’t have had to invest in their standard sized round brushes as well.). The Voyager brushes are abut 1-¼” longer than the others when closed, but the upside is that when you open them up, you’ve got a really comfortable full sized brush in your hands.
I just ordered some travel brushes from Rosemary & Co., primarily because they are the only company I’ve found that had more than just rounds in their travel brush line. They haven’t arrived yet (and I have no idea how long it will take as there are no retail outlets in the US and I had to order form the UK) – but if you’re still deciding when they get here, I’ll be happy to give them a test run for you.
[Photo: The gold metal case is #2 Whiskey Painters, silver case is the #2 Winsor and Newton, the blue brush is a Cotman synthetic….came in one of their field kits… has medium tip control but holds less paint than the others… Black brushes are the Black Velvet Voyagers.
Hope this is helpful!