Depending on the project, you want to quilt, the thread types available each have something special to offer. The best way to learn about threads is to play with different ones and discover the effects each will have in various situations.
One important tip to keep in mind is you should always be able to break the thread by pulling on it between your two hands. If you cannot break it, do not use it for quilting! It is actually too strong and in time will wear and perhaps cut through your quilt. Put it to use in the garden to support your plants instead.
Threads come in different weights. Unlike when you step on a scale, a smaller number actually signifies that the thread is thicker. Remember, the smaller the number, the thicker the thread and the higher the number, the finer the thread. A spool of thread that has 30 wt on it is going to be thicker than a spool of thread that has 40 wt written on it. Keep in mind that needle sizes work like dress sizes which is the opposite of how thread works. The lower the size on the needle the smaller or thinner it is, and the lower the weight of thread the thicker it is.
Ply is another word used to describe thread. A ply is one strand of thread and one-ply thread will naturally be a very weak thread. Three-ply thread is three strands of thread twisted together and will be a stronger thread.
It is important to consider the characteristics of thread types when choosing which to use in your quilting project.
Cotton thread is a natural fibre and has been around forever. Commonly used in many piecing and quilting projects it is available in various weights.
Polyester thread is a man made fibre. It is quite a strong thread.
Rayon thread is generally considered a natural fibre. It is also a strong thread. When used in quilting it has a beautiful shine that looks a little like silk.
Metallic thread is a man made fibre. Historically this thread was actually fine wires of gold, silver and copper. Nowadays the fibre content of metallic thread is not usually so exotic but rather polyester or a polyester and nylon blend.
Silk thread is a natural fibre (and probably one of the most expensive threads). It looks exquisite when used for quilting designs on quilts