When is a red card permanent, and when can the player be replaced after 20 minutes?

Law 9.30 (elite rugby only):

• Permanent red card: for intentional and highly dangerous actions. The player takes no further part and cannot be replaced.
• 20-minute red card: for other sending-off offences. The player cannot return, but any available replacement may come on once 20 minutes of playing time have passed since the incident. Under World Rugby's guideline this can be any member of the bench, used or unused (subject to Law 3.33).

Only the referee can show a permanent red card, either directly on the field or after a normal on-field TMO review when the outcome is clear after a short number of replays. An FPRO or TMO conducting an off-field review cannot recommend a permanent red card.

In non-elite rugby, every red card is permanent and the player may not be replaced.