I would hazard a guess you have to use their proprietary material to inject into your mold.
“This allows you to mold soft plastics (which you can buy from the company, also called Saltgator, or a hobby shop or fishing-lure supplier) and mold a piece up to 250mL (8.4 oz) in volume in about 15 minutes.”
Can I use materials other than your SoftGel?
Yes. While we’ll offer our own optimized SoftGel formula, SALTGATOR is not locked to proprietary materials. You can experiment with other low-temperature thermoplastics that match our safety and flow specs.