Ultrabond® Sealant 721 is a UV curable adhesive that can be used to seal a variety of plastics when exposed to UV light. The sealant offers a water- tight seal with excellent environmental resistance. Prevents material escaping through a crimped seal. With Ultrabond® Sealant 721 a low powered UV lamp (Blacklight), can be used to inspect for the presence of adhesive on the substrates.