Long Or Short Nap?
The "nap" on a paint roller is the hollow cylinder cover, usually made of off-white or cream-colored fibers, which slips onto the roller itself. Basically, it's the part of the roller that puts the paint on the wall. Naps can usually be bought separately from the roller handle, meaning that you can use the same handle with a variety of different naps, according to the requirements of your painting task.
When it comes to choosing the best nap for your paint job, the length of the fiber is crucial. Different types of surfaces require different lengths of nap. Using the wrong nap length can leave excess paint on your wall, or make it difficult for you to distribute the paint evenly. The basic rule is that the smoother the surface, the shorter the nap, and vice versa. What follows are some general guidelines for choosing the correct nap length:
A short nap (1/8 to 1/4 inch) is best for smooth, flat surfaces such as very smooth plaster, hardboard, wallboard or sheet rock.
A medium nap (3/8 to 1/2 inch) is best for slightly textured surfaces such as sand-finished plaster, poured concrete and rough wood.
A slightly longer nap (3/4 inch) is good for textured, rougher surfaces.
A long nap (1 to 1 and a 1/2 inches) is best for very rough surfaces such as concrete blocks, bricks, cinder block, corrugated iron, asphalt and wood shingles (generally these are outdoor surfaces).
If you're unsure as to which category the surface you want to paint falls into, remember that most interior surfaces are in the range of the 3/8 inch medium nap.
It's not just the length of the nap that will affect the quality of the paint job - the type of fiber it contains is important too. Different fibers are appropriate for different types of paint. Naps made of synthetic, man-made fibers are good for latex paints. Naps made of natural wool or lamb's wool are best for oil-based paints. Mohair naps work well with enamel paints.
Selecting A Nap
By the time you get to the store, you should already know which type of surface you're painting and which length of nap you need. When looking at the naps available, there are a few things you should check in particular:
Is the nap core made of cardboard or plastic? Plastic cores are, without doubt, more practical and longer-lasting. Cardboard soaks up the paint and becomes soft and useless. If you take good care of a plastic-core nap, you may be able to use it for several different paint jobs, the same cannot be said for naps with cardboard cores.
Does the nap material have any visible seams or joining lines where it has been sown together? If so, don't buy it - look for something at a higher price with better quality. Seams and lines on a cheap nap may end up being imprinted on your wall!
If you squeeze the nap, does the fiber pop back into place as soon as you let go? This is another indication of a good quality nap. If the fiber remains depressed, you need to look at something higher up the price range.