Tip and tail spacers
Quotes are verbatim and attributed to their original authors.
Where the tip and tail rise, the wooden core is too thick to bend, so builders splice in a thinner, bendable spacer between the core and the tip. It is a small part with an outsized effect on how easily the tips form and hold their shape.
What to use
The default is roughly 2 mm P-tex, running edge-to-edge with the core so no wood extends into the tip. Cheap, effective alternatives abound:
Builders also build very tough spacers from several layers of fibreglass. If you use base material or P-tex, prep it like any bond surface: "just make sure to sand it with 80 grit and flame the crap out of it" (#3603).
Full-wood and bamboo tips
You can skip the spacer and run the core wood (or bamboo) full length — the catch is thickness:
Planing wood that thin on a benchtop planer invites vibration and tearout, which is a large part of why a separate P-tex spacer is the easier path — especially on a vacuum press, where thin tips are needed to hold tip height.
Holding it in place
The spacer is simply set into the layup butted to the core; hold it during assembly with tape, hot glue, super glue, or staples out on the waste edge that gets trimmed off. Bond and resin matter here too — early delaminations on the forum were traced to "poor bonding with ABS tipspacers… the abraded p-tex works well" (kam).