If by give, you mean bend easily, something stiffer is probably better. Bendy never sounds good.You should absolutely add a layer of pipe foam, or similar density foam, along the striking edge, especially if using a denser foam as the bulk of the blade. Open cell foam over dense foam would be like open cell over bare pipe. Also, I have heard that when used along a blade edge, it tends to deform easily and lose its nice shape.Even though you likely won't be thrusting with it, don't forget to cut the pipe a few inches shorter than the foam of the handle, in case of accidental collisions.
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