Ampac Extra Strong Oxo-Biodegradable Polythene Envelope 240x320mm C4 (Pack of 100) KSV-BIO2. Ampac Extra Strong Polythene Envelopes are resistant to tearing helping your contents arrive at their destination safely. Polythene is extremely strong without being heavy, meaning that these envelopes save you money on postage costs - especially when mailing in bulk. These envelopes are also oxo-biodegradable, helping to protect the environment. These C4 opaque envelopes come in a pack of 100. Tear-resistant polythene envelopes. Peel and seal closure. Oxo-biodegradable to protect the environment. Size: C4 (240x320mm). Pack of 100 envelopes. Opaque.