An M-type inflatable bag (1) includes a bottom wall (11), two side walls (12), two protective walls (13) and two connecting portions (20). The bottom wall (11) includes a plurality of bottom gas columns (111). Each of the side walls (12) includes a plurality of side gas columns (121). Each side wall (12) is located on two opposite sides of the bottom wall (11). The side walls (12) and the bottom wall (11) are divided at a joint to form a receiving space (O) and a limiting space (R). The protective walls (13) include a plurality of protective gas columns (131), and the protective walls (13) are separately located outside the side walls (12). The connecting portion (20) includes a plurality of first heat sealing nodes (171) adjacent to the side wall (12) and a plurality of second heat sealing nodes (181) adjacent to the bottom wall (11). When the side wall (12) and the bottom wall (11) are bent, a buffer bump (21) is formed between a first virtual bending line (L1) and a second virtual bending line (L2).
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