suggested u take superlon..insulflex's material are harder and it will crack more easily than superlon if expose to high temp(less durable)

SUperlon has 6mm and 10mm both with and without self adhesive. I had 10mm superlon stuffed inside my door plastic panel, bitumen strips on the metal panel ( you need to take out the weather plastic sheet first), swimmers kickboard on the wheel arch which is atype of closed cell foam too.

basically soundproofing is
soundproofing = sound insulation + sound dapemning

sound insulation - to prevent noise from entering cabin, absorb low frequency and bassy noise ( road noise, other noise)...dampening is to add weight to the metal parts of a car to prevent it from vibrating which could produce hi frequency noise (stones hitiing the chassis, rain drops)

Frankly speaking not sure if there's improvement, but closed cell foam like superlon could mute sound from speaker ( to test a foam's sound isulation property, just cover a speaker with the foam) and water resistant... .. since that wira's already an established model, go get hayness manual to take out the plastic covers without breakign any plastic clips...DIY sound proofing is a trial and error process. take your time to do it.

you could get the superlon from a trader at zerotohundred...i thought both superlon and insulflex are made of same materials.