It sounds like you are trying to sheath cables?
o Use expanding nylon braid for around the cables
---- expands as large as you want
o Use adhesive lined heatshrink for the ends only
---- glue melts into the braiding to stop it coming apart
---- plain heatshrink can slide off the braiding

That will retain flexibility except around the adhesive
lined heatshrink ends which will be a bit rigid. That can
be minimised by using very short pieces of heatshrink,
since it is the glue that seals the nylon braiding together.

Spiral wrap comes in several sizes - small o.d. to large o.d.,
the large o.d. is useful re cables exiting everywhere (5.25").

Self amalgamating tape is for outside applications really.
It is not really suited here, it can make a right mess.

Try to aim for 3:1 low temp heatshrink vs 2:1 high temp.
Quality heatshrink costs a little more, but is worth it.

Alternatively use...
o More cable ties along the cable to keep wires bundled more
o Velcro cable fasteners to bundle cables up as needed

Most supermarkets carry pk5-6 velcro cable ties for 79-99p.
They work well re not damaging cables, easily undone/redone.

To join wires - spiral-bare-ends-into-one-another vs overlap-twist,
it results in a better connection, less sharp points thro heatshrink.
Note very large heatshrink will readily split on any sharp objects,
and becomes rigidised (shrink increases wall thickness), so it is
far better to use nylon braiding than heatshrink for sleeving.
--
Dorothy Bradbury
www.dorothybradbury.co.uk for quiet Panaflo & NMB-MAT fans