Why do the foils sometimes heat up and puff up?

When there is a presence of iron or metals in the hair usually from well water or some home colors, the color in the foils may heat up slightly or puff up.

When there is a presence of iron or metals in the hair usually from well water or some home colors, the color in the foils may heat up slightly or puff up.  Also in the presence of metals, the color may become runny while under the heat.   If the presence of metals is suspected, a test strand is necessary.  Before the FRAMCOLOR 2001 LIGHT&SHINE application, some clients will need a demineralizing treatment to eliminate the build-up of these metals for a successful color service.  These results will be observed when coloring these clients with any color, but are more noticeable with FRAMCOLOR 2001 LIGHT&SHINE because of the usage of heat.