PROBLEM: Prime towers tend to collapse when two materials that do not stick to each other are used.
POTENTIAL SOLUTION: what about printing a tower where the two materials are in "concentric" squares each made of one material only ? This way each material would have to stick to itself (see drawing, a=PETG, b=PVA, "." = no material) copy paste into notepad to see with correct char spacing).
Double the material will be used, but it is worth it vs having a collapsed tower.
Layer 1
aaaaaaaaaaaaaa
abbbbbbbbbbbba
ab ba
ab ba
ab ba
ab ba
abbbbbbbbbbbba
aaaaaaaaaaaaaa
Layer 2
aaaaaaaaaaaaaa
abbbbbbbbbbbba
ab ba
ab ba
ab ba
ab ba
abbbbbbbbbbbba
aaaaaaaaaaaaaa
Layer n
aaaaaaaaaaaaaa
abbbbbbbbbbbba
ab ba
ab ba
ab ba
ab ba
abbbbbbbbbbbba
aaaaaaaaaaaaaa