aluminum ducts with cooltubes?

i just got my cooltubes not to long ago and with 6 1ks my plastic styleflex duct heats up and stinks are there chances it goes on fire? and i better off to use alum flex duct. i think the shit will probly end up leakig air quicker with the constant bending from raising and lowering the lights.

is it safe to use normal ducts or should i opt for aluminum expanding flex ducts?

Aluminium all the way. The grow shop people should have sorted this, the plastic stuff cant take the heat without at the very least outputting toxic fumes, and worst case senario, melting.

Fire hazard you need to fix immediately. They have flex stuff suitable for high heat that won't break.