Retraction Extra Prime Amount
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Even if the filament is retracted, you sometimes still lose some material on the way. This setting compensates for that by moving the material a bit further in than how far it was retracted.

The higher the extra prime amount is, the more pressure is added in the nozzle chamber after a retraction, which helps for the loss of pressure in the chamber. If the setting is too high, it will lead to blobs in the place where the nozzle lands after a retracted travel move.

This is particularly useful for flexible materials, which tend to take more time to retract. During this time it'll ooze more, so more material is lost.