We are trying to create carbon wing (see photos) from textrem with infusion, almost whole wing is ok, but last part, after few minutes on sun it goes wrong.

Can you please give us some hint, what we are doing wrong?

So I couldn't find a lot of information about the resin system, but I did find that it's styrene based so obviously vinyl ester or polyester. Is this a resin designed for infusion or vacuum bagging? If not, this might be your issue. Styrene based resins require the styrene monomer to cure properly, but under vacuum the styrene evaporates too quickly and doesn't let the resin cure fully.