Released to mark Penguin Books’ 80th birthday, the pocket-sized, 80p-a-pop Little Black Classics have been a hit, selling 70,545 copies in the first week of publication.

The commercial success of the commute-length gobbets – 80 titles ranging from the Communist Manifesto to Sappho’s poems to Mozart’s letters to his father – is striking since they are all in the public domain. To quote a commenter on the Guardian website: “How many of these are not available in full on Project Gutenberg?”

How to explain the appeal? Partly it’s the curation; but it also proves people like their reading matter cheap… and portable.

Portability can be overlooked in print publishing. I’ve noticed a mini-trend for mammoth print bundling, combining, for instance, the entire set of Nancy Mitford’s novels or the Patrick Melrose series in one giant book. You can understand why someone might buy one (“that would make a nice present”) but have publishers considered the actual reading experience? The typeface is tiny. They are too big for a handbag; too heavy to read while relaxing in bed or in the bath.

I need to judge books by their weight. Like many people, most of my reading is done on the move. For me, on the move means hulking around a laptop, a dog and standing up on public transport. I need something I can read with one hand in a confined space on a packed train, which limits my options to a slim paperback, mini tablet or e-reader.

The controversy over ebook pricing has blinded us to the major boon of e-reading: its portability. Some publishers have reacted against digital by making physical copies even more desirable: strokable covers, coloured page edges, sticker sets. Beautiful objects with a high RRP to match. But doesn’t our behaviour both online and offline indicate our desire for the opposite: low-cost and utilitarian?