I don't have expander pellets in my country. I want to make them for myself. I have used them last year and caught 378pouns of fish in a 9hour session but I have only used them twice. The thing is the dealer that bought me those Passed away and after that I haven't found anybody who would bring me those.I reckon they're just floating pellets forced to sink with the use of a pump.
There are pellets available now that don't need pumping, Sonu pro expanders.
Pumping is not compulsory, just a soak in water to soften them is all that's really needed, hook one then give it a squeeze in water for a slower fall.
Why do you need to know, are you trying to produce them.