These are equivalent to mail lite/feather-post size B - the internal measurements of each envelope are 115mm x 195mm. Classed by Royal Mail as 'Letter' size. 500 x Size B (00) Jiffy Aircraft Padded Bubble Envelopes.
500 x Jiffy Airkraft Size 00 (B) Padded Envelopes 115x195mm[5055502318240]