A network device implements a foldable ingress buffer for buffering data units as they are being received. The buffer is organized into a grid of memory banks, having different columns and rows. A Transport Data Unit (“TDU”) is stored interleaved across entries in multiple banks. As each portion of a TDU is received, the portion is written to a different bank of the buffer. In each column of the buffer, a full-sized TDU has portions in a number of rows equal to the number of folds in the buffer. The sum of the bank widths for each row thus needs be no larger than half the maximum TDU size, which further means that the number of columns in the grid of banks may be reduced by at least half compared to non-folded approaches, with little increase in the number of rows, if any, depending on blocking and reading requirements.