The seam is one of the most honest quality signals on a softgel. It is the line where the two shell ribbons are pressed and sealed together in the rotary die. If the seal is uneven, thin, or poorly fused, the capsule is more likely to leak, split, or fail during drying and handling. A clean, even seam is a sign that the shell formula, tooling, and process are well matched.
This short clip holds two plant-based softgels side by side. On the left is the AMYLOM plant-based softgel — a gelatin-free hydroxypropyl starch shell — shown next to a competitor sample. The close-up in the middle of the clip lets you look directly at the seam line and the overall shell clarity of each capsule.
What a good seam tells you
In rotary die encapsulation, two shell ribbons meet over the fill and are sealed by heat and pressure as the dies rotate. The quality of that seal depends on ribbon thickness, shell temperature and elasticity, fill behavior, and die alignment. A well-made seam sits flush with the capsule body, with no visible gap, fin, or weak point along the seal line.
Gelatin-free shells behave differently from gelatin during sealing. Hydroxypropyl starch has its own gelling, elasticity, and drying profile, so the process has to be tuned specifically for a plant-based shell rather than borrowed from a gelatin recipe. Producing a consistent seam on a gelatin-free softgel takes a process that has been tuned for the shell over many runs, not adapted on the fly.
Shell clarity and consistency
Beyond the seam, shell appearance is part of the finished result. Clarity, surface evenness, and a uniform wall come from the shell formula and the drying curve. These details are easy to miss in a spec sheet but obvious when two capsules sit side by side.
AMYLOM (Amylom Biotechnology) develops hydroxypropyl starch shells and runs plant-based softgel encapsulation for supplements, gel candy, and specialty formats. See our softgel capabilities or talk to our team about a plant-based softgel project.
