Accu-Cast makes a good number of alginate formulas. This is because there are so many different types of projects people like to do. We are NOT a "One Size Fits All" compromise type of company so the following information will help you decide.
TWO TYPES OF MOLDS
There are two basic types of molds- Bucket Molds and Layup Molds.
Bucket Molds are when the mixed alginate is poured into some type of container and the object (body part) is submerged into it. Hand casting is a perfect example of a Bucket Mold. Ideally the alginate is thinner for a Bucket Mold so it flows nicely around the "object" as it is submerged. Ideally the alginate sets to a very flexible rubbery consistency so the "object" is easily removed without tearing the mold.
Layup Molds are when alginate is applied to the outside surface of the skin in a thin layer. Face casting and torso casting are perfect examples of Layup Molds. An ideal alginate for a Layup Mold is thicker and resist dripping. It should go onto the skin more like cake frosting rather than pancake batter so it is easier to control and less is wasted.
The other factor that determines an alginate's ideal suitability is the size of the project. Bigger, more complex projects require longer setting time than smaller projects. Our alginates set in a range of times from 2 minutes to 10 minutes.
Obviously a beginner requires more time than an expert to mix and apply the alginate. If you are new to LifeCasting, PLEASE don't underestimate how much time you will need. "Its always better to have a little extra time, than not quite enough".
Our alginate numbering system is important. Our (570) alginate sets in 5 minutes when using 70°F water, where our (380) alginate sets in 3 minutes with 80°F water.
Ultimately personal preference is the most important factor, but until you get to know our products well enough for that, here's a quick guide.