Carry On Bags:
Yes (Less than or equal to 3.4oz/100 ml allowed)
Checked Bags:
Yes (Special Instructions)
Formaldehyde solutions of less than 10% are not restricted as hazardous materials. Leak-proof packaging with absorbent material is still strongly encouraged. For formaldehyde solutions containing more than 10% formaldehyde, see separate entry for "Biological specimens in preservative solutions."
Tip: Full-strength "Formalin" is typically 35%-40% formaldehyde by volume. So a solution that is less than 25% Formalin would be less than 10% formaldehyde and not restricted.