I've tried brushes made of different fiber bristles and found the best
to use, at least with my enamels, are the brown natural soft fibers.
Whenever I need to replace one (usually because my wife borrowed it for
her canvas painting LOL) I check at my department stores craft
department or hobby shop. I have brushes that range in price from $3.00
to $7.00 US. I bought my son a set from Wal*Mart (our local department
store) in their crafts section for around $5.00 or $7.00 and it had
around eight brushes in it. It came with a small size of 0 I think, but
I have a few 30/0's and/or 000's that we can use.
Look for those brushes that are marked for "Oil Paints".
Stay away from those that you can buy 30 for $2.00 US, the ferrules
[right word?] fall off the handles when cleaning/drying the bristles on
a paper towel.
Spend the extra money for a decent brush and take care of it, they can
last almost forever. I still have a few that has lasted for 37+ years
and seen hundreds of models or painting projects. Not a bad
investment for a $4.00 paintbrush instead of a $1.50 one.
Oh, the only thing I've found those Testor paint brushes good for,
stirring the paint when I run out of toothpicks. If anyone knows of
what else they can be used for, please... I'd like to know.