Envelopes
PostSafe ltd P27 Envelopes Extra Strong Opaque 400x430mm PK100
Postsafe extra strong, extra durable, lightweight and waterproof polythene envelopes Suitable for heavier items A special white panel accepts any endorsement Peel and seal closure Opaque Size: DX (30 x 400mm).
https://www.bizrate.co.uk/envelopes/postsafe-ltd-p27-envelopes-extra-oid40095572100.html