Do you know the way thermal binding works? If no, I will tell you now. The pages stick to a layer of glue so that they are held together. If you want to use the machine, you need to have thermal binder adhesive. There are a variety of forms which can fit with this material. You should learn about all the distinguish options so that you can have the right decision when choosing.
You can opt for a ready to use folder, also called cover. It has glue on its spine, so you do not have to worry about adding it yourself. This is by far the simplest choice. The folders are functional and easy to use. Furthermore, some machine work only with such materials. Another benefit is that you can choose from all sort of folders paper, plastic, hardcover linen and leatherette ones.
The next option is to get thermal binder adhesive strips. These have glue on both sides. You simply take a piece and stick it to the spine of every folder that you like. This is a great option, if you have special folders that you would like to use for book assembly. You can easily do some cutting to make the strips suitable for any spine, irrespective of its size. Still, the quality of binding will depend on the quality of the strips as well as on how well you apply them.
Your third option is to get thermal binder spines covered with adhesive. You can use these materials to make your own folders with any covers that you like. This is probably a better option than using glue sticks. The spines have specific designs that allow for the books to be bound perfectly and to last for a long time. Despite this, given that the front and back cover are also attached to the spine with glue, the folder might be flimsy and more prone to tearing and damage.
Overall, it is up to you to decide which type of thermal binder adhesive to use.