A "Pourable" mold rubber is mixed and poured over your original model.
Consider this method if your model is;
Advantages/Disadvantages - Pourable molds are easier to make vs. brush-on molds, requiring less labor. They also take less time to make, meaning you will have a mold you can use same day or early next day; however, you use more material to make a mold so your material cost is higher.
A "brush-on" mold rubber is mixed and brushed onto your original model in layers. After all layers cure (usually overnight), a rigid support shell (also known as a "mother mold") is applied the next day.
Consider this method if your model is:
Advantages/Disadantages - Less material, over all, is used to make a brush-on mold so your material cost is less. However, Brush-On molds take more time and effort to make (much more labor vs. a pourable mold). Making a brush-on mold is also more challenging and therefore requires a lot more pre-planning.