Retail booklets - a study of the paper thickness

I remarked when describing the Queen Retail Booklet, that the whole thing seemed to be not as

thick as previous booklets.  Later there was confirmation that other booklets were also on thinner paper.

Stuart Leigh, who produces the catalogue of Post and Go stamps, confirmed that there were variants, and set to work with his micrometer.  Stuart kindly shared his findings which are reproduced below: but I would not be surprised if other people come up with different findings for some of the booklets, especially those other than the mixed-content (MCIL) booklets which have reprints.

	Thickness of Backing Paper	Thickness of Backing Paper + stamp
	(ins.)	(ins.)
RAF 100	0.0045	0.0085
Red Arrows	0.0045	0.0085
Dad's Army	0.0045	0.009
Hampton Court Palace	0.0045	0.0085
Poppies	0.0045	0.0085
Harry Potter	0.0045	0.009
Harry Potter SBP1 inverted	0.0045	0.0085
MARVEL Super Heroes	0.0045	0.009
Birds of Prey	0.0045	0.0085
D-Day Landings	0.0045	0.0085
Elton John	0.0045	0.0085
Royal Navy Ships	0.0045	0.0085
Star Wars	0.0045	0.0085
Tomb Raider	0.0045	0.009
James Bond	0.0045	0.009
Coronation Street	0.0045	0.009
Queen	0.004	0.008
MFIL M18L - 2nd Class	0.0045	0.0085
MFIL M19L - 2nd Class	0.0045	0.009
MFIL M18L - 1st Class	0.0045	0.0085
MFIL M19L - 1st Class	0.0045	0.009
MTIL M18L - 2nd Class	0.0045	0.0085
MTIL M19L - 2nd Class	0.004	0.008
MTIL M18L - 1st Class	0.0045	0.0085
MTIL M19L - 1st Class

While concentrating on the printing on the backing paper (for instance on the Harry Potter booklet) I didn't notice any change in thickness, but then it wasn't immediately obvious.  The combination of thinner stamp paper and thinner backing paper is what made it more obvious (to me) for the Queen booklet.

What's also interesting is that the findings show that stamp paper thickness has changed, but not in any consistent way.  One might have expected thinner paper for economy purposes, but the M19L Large stamp booklets are actually thicker than the previous one, while the 2nd class booklet of 12 has both backing and stamp paper are thinner.

The backing paper on business sheets and counter sheets is thinner than that used for booklets, but given that Walsall now print all of them, it seems possible that the stamp paper used for these could also vary and may already have done so.

I'll happily report your findings, although I do not have the equipment to check stocks, and cannot supply variants.

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