There are many different blades on the market therefore it is not always easy to know which blade to use:

First thing to consider is what type of wood you are going to use, hard or soft wood?

Second is, what thickness is the wood?

Third, what are you going to make: just scrollsawing or more detail work with many inside cuts, which by the way is called "fretwork". When doing just outside cutting, which no longer can be done by a bandsaw, it is called "scrolling".

Most companies use the following number system, from 3/0 to 12. Metal and jewelry blades might start as low as 10/0. The lower the number the finer the blade. For thin wood use the lower numbers, use a low feed rate and remember, they break more often.
For thicker and harder wood, use the higher blade numbers. The blades with less TPI (teeth per inch) will cut more aggressively. For example, a blade with 8 TPI cuts faster than a blade with 12 TPI, however there is more control with a blade that has 12 TPI.

Then there are the blades with reverse teeth. Some of the Flying Dutchman blades have reverse teeth. Blades with 12 rev. teeth will burn the wood more easily and do not clean the kerf as well as blades with less rev. teeth. They create friction and heat the blade, therefore you don't get the use out of the blades.
Some blades have double teeth, with and without rev. teeth. There are people who prefer them over the single teeth blades. You might have a little more control.

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Now we have the straight teeth blades, most of them are called skip-tooth blades. Here again it is up to people and what they get used to. They will leave enough fuzz on the bottom so that you will have to sand it off. They might follow the line easier while sawing. They clean the kerf very good and therefore less chance of burning. The blades with two teeth down and one up are maybe the best for splinter free cutting and might be one of the best to use with plastic but you should use 2" clear packaging tape over the pattern for burn-free cutting and so that the plastic does not melt back together.

Everything depends on the level of experience and what project you are making. Also, it depends if you do any stack cutting. The best way is to experiment with some different blades. When working on a project you might start with a #3 FD-SR and find that a #5 or #7 might do a good job for you. The higher the number the less breakage you will have in the end.

Article provided by Mike Moorlach o