The test piece I didn't seal. I was just curious how easy it would be to catch on fire in case I missed a spot with the Thermo Tec seal. My headers I did seal and did the foil just in case. The foil also adds some more insulating properties. It was $3 for a box of foil and $2 for some wire which covered the entire header so it was cheap insurance. I didn't have any problems with the foil damaging the wrap. You can also purchase the wrap with the foil from Thermo Tec and other wrap companies.