A4/C4 White Do Not Bend Envelopes combine a 600gsm rigid backing to eliminate folding or bending during transit with a strong and presentable 120gsm white paper front with “Do Not Bend” printed in red to encourage safe and careful handling of your mail. These cardboard envelopes have a strong peel and seal adhesive strip closure to keep the contents of the envelope secure whilst in the post and helps keep your packing time to a minimum.