Background story

In my old thermos the cap's sealer broke into three pieces:

So I reverse engineered the cap's sealer in FreeCad.

The initial MK1 model has been designed exactly as the original sealer, but it was not rigid enough at the bottom part, so the MK2 has been made.

UPDATE

Tested with PLA PRO, but still after using boiling water the cap's sealer deform.

Printing details

Printing

Print with bottom on build plate standing.

Filament - ABS

Infill - 80%

Layer Height - .15mm to .20mm

Supports - Needed for MK1

Perimeters - None

Additional Parts - None

Bed Adhesion - You may want some glue stick to ensure good bed adhesion, but in general it's not needed.

Rafts - None

Scaling - None

Filament Change - None

Post Printing Notes:  May need some grinding.

!WARNING!

Tested with hot hot tea, and unfortunately the cap's sealer went pliable.