Will Call is probably right. DME collapsible core may do, but all about the cost.
Dwight's more conservative, but may save you more on the tooling cost if the under cut is not too much, say 0.6 or even more for some materials like TPR, EVA. With the right plastic material, there is a chance that it is very possible it can be extracted from the tool.
By the way, the collapsible core Will mentioned belongs to the pre-enginerred components category in DME's catalogue.
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