This is my understanding of tubular glue and such:
Tubular glue is a contact adhesive. Basically, the molecules in the glue form these strands that when wet are straightened out, but when the solvent dries off, these strands start kinking up and connecting to each other. Calvin Jones explained to me that it's kinda like velcro. lots of thin layers are recommended because basically it means these molecules (I wish I could remember what they're called) can kink together more. Think of it like a really dense sponge vs one with really big holes everywhere.
Most tubular tapes are bad because they're just like double stick tape. They don't have that mechanical bond that glue has. Also, most tapes are really narrow compared to modern rims and tire base tapes. The point of highest stress on a tire is right at the edge of the rim.
This brings us to cyclocross tubulars and tape. Rim shapes are designed to match the profile of the tire that's meant to be glued on, to increase contact area of the adhesive. That's why if you pump up an old timey 16mm tubular on something like a velocity major tom, you'll see a big ol' gap between the rim and tire. It's just not meant to mate. Now if you consider a traditional 19mm rim was designed for a 23mm tire, if you bump that tire up to, say, 38-40mm you'll have the opposite problem. The edges will touch, but the center won't snuggle up to the rim. That's why cx tape is used. It fills out that void to give that full contact area.
Which brings me to the last part, why do we use multiple layers? Because the surface irregularities of tires mean that if you only had one layer, there might be areas where the base tape and rim just don't contact. Building up a few layers (I do 3-4 thin layers) makes up for those surface irregularities.
And that's my story about tubular adhesives.
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