Both are silicone, but they behave differently in production. Solid silicone is a high consistency gum that is milled, weighed and pressed. LSR is a pumpable two part system that is dosed automatically, injected into a closed tool and cured in seconds.
That difference decides the economics. LSR needs a more expensive tool and a more expensive machine, and pays it back through cycle time, low scrap and very little manual handling. Solid silicone wins on tooling cost and on large flat parts.
LSR also reaches into detail that compression cannot fill, which is why micro valves, thin membranes and baby nipples are almost always LSR.
Tell us the part, the material, the hardness and the annual quantity. We will come back with a process recommendation, a tooling proposal and a piece price.
