It is the blade you install in your jigsaw that determines the quality of cut the tool is capable of making.
It is critical that you choose a blade suitable for the material you will be cutting. In addition, you should consider the TPI of the blade you select, as the finish it produces will depend upon how many teeth it has.
Material
Thinner materials should be cut with a blade with fine teeth. The thinner the stock, the more teeth necessary.
How hard a material is will also affect the type of blade that will most effectively cut it. The blade must be made out of a material harder than that of the workpiece.
Softwoods
Blades designed to cut through wood have large and sharp teeth. Low- to medium-duty cutting through softwoods can be done using a blade made out of high carbon steel.
If you will be using your tool for an extended period, a more durable bi-metal blade will last longer before it becomes dull.
Hardwoods
Because they are harder, hardwoods like oak or ash require a stronger and more durable blade.
The most effective jigsaw blades for cutting through hardwoods are made out of high speed steel or bi-metal.
Metal
Cuts in metal (or nail-embedded wood) require a blade made out of either high speed steel or bi-metal.
In addition, the blade should have very small, closely-spaced teeth, with a TPI of at least 14.
Plastic
Softer plastics can be cut using blades made out of high carbon steel.
If, however, your workpiece is made out of hard plastic, a bi-metal blade will be able to more efficiently complete the job.
Tile, glass or brick
If you are cutting extremely hard, abrasive materials such as ceramic tile, glass or brick with your jigsaw, you should use a tungsten carbide blade.
Because the cutting edge is tooth-less, the blade will not chip or damage the workpiece.
Type of cut
Rough cuts
For faster and rougher cuts where the overall finish is not important, choose a coarser blade with a lower TPI.
Because these blades have less teeth, they are able to remove more material each time they move up and down. This means that they are able to cut through a workpiece more efficiently.
Clean cuts
If you are looking to make a clean and accurate cut, you will need a blade with smaller, closely-spaced teeth.
As they cut less aggressively, blades with a smaller TPI produce a neater, more-controlled cut.
Straight cuts
Straight cuts are more effectively made using a thicker jigsaw blade, perhaps made out of high speed steel or bi-metal.
This is because a thicker blade will be less likely to bend away from the cutting line.
Curved or scroll cuts
To make intricate curved or scroll cuts, you will need a special scroll cutting blade.
These blades are slightly narrower than normal to allow you to more easily manoeuvre it through the workpiece.
Plunge cuts
When making a plunge cut (without making a starter hole), perhaps in order to make a cut-out in a kitchen worktop, you will need a blade that has a pointed end.
This sharp tip will ensure that the blade is able to slowly penetrate the workpiece before continuing the cut.