FDM internal structure image

SLS and MJF 

If your part needs to be free from un-sintered powder then any hollow sections without an opening in the design will need to have a drain hole added and bonded into place after the manufacturing process. Without the drain hole the un-sintered powder is impossible to remove and will remain contained within the part. It may be necessary to hollow parts to reduce warping during the print process (see Hollow Sections).

Powder Removal Diagram
(Click image to expand)

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