A few snippets from the below PDF on tube production.
Advantages of butyl innertubes to end users (vehicle owners)
In summary, use of butyl rubber innertubes offers a number of
advantages to the tire end user such as:
• Consistent inflation pressure.
• Reduction in tire rolling resistance, due to the better
inflation pressure retention, which may improve fuel
consumption.
• Longer tire life and more even-wear performance.
• Longer innertube life due to better heat stability.
• Enhanced tire durability.
....
Low modulus innertube
The concept of “low modulus” innertube compounding is an
important parameter for innertubes designed for service in
radial ply tires. Radial ply tires have a longer service life than
bias ply tires. Moreover, the radial ply construction of such tires
results in a higher degree of flexing of both the sidewall and
the innertube fitted inside the tire. Thus, not only must the
innertube last longer in a radial ply tire, it must do so under
conditions that results in a higher stress on the innertube walls
and particularly the innertube splice. In this regard, when
compared to general purpose rubber innertubes, the
advantages of low modulus butyl rubber innertubes could be
listed as follows:
• Compound processing:
- Good flow and green tack, and,
- Improved splice properties.
...
Guidelines for splicing
Splicing, like mixing, is an important step in butyl rubber
innertube production and should be performed as efficiently as
possible, since splice faults often form a large proportion of
total rejects. The worldwide trend of increasing use of radial
ply tires has meant that greater performance demands have
been made upon the innertube splice which must withstand
the higher degree of flexing of the radial tire sidewall and the
innerliner splice must continue to do so throughout the much
longer life of a radial tire.
https://www.exxonmobilchemical.com/~...nual_enpdf.pdf