`Binary | Hex | Dec | Field`

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0b00001 | 0x1 | 1 | bulletproof

0b00010 | 0x2 | 2 | fireproof

0b00100 | 0x4 | 4 | explosion-proof

0b01000 | 0x8 | 8 | collision-proof

0b10000 | 0x10 | 16 | melee-proof

0 means no immunity to any damage, 31 means immunity to all damage. You can add all the numbers together or use bitwise OR/AND to toggle flags.