New Guardian Heavyweight Manilla Board Backed Envelopes. Send documents with confidence in these high quality manilla board backed envelopes which provide a combination of good looks and strength. Exceptionally strong 130gsm ribbed manilla paper across the whole range. Subtle ribbed texture and distinctive sheen provides an attractive finish. Backed with a sturdy board to keep contents flat and protected. Printed Please do not bend instructing considerate handling. Peel and Seal gumming for an exceptionally strong seal. Window: 40 x 100mm 25mm in, 213mm up. Size: C4 324 x 229 mm. Packed 125.