The NEXTFLEX® Universal Blockers are designed for use with Illumina® indexed adapters. They are effective in blocking single-indexed or dual-indexed libraries, without being affected by index length or the presence of a unique molecular index (UMI). The NEXTFLEX® Universal Blockers are designed to target both strands of the adapter sequence regions. The NEXTFLEX® Universal Blockers are compatible with ligation-based workflows, such as the libraries prepared with NEXTFLEX® DNA Barcodes, NEXTFLEX-96™ DNA Barcodes, NEXTFLEX HT™ Barcodes, NEXTFLEX® Dual-Index Barcodes and NEXTFLEX® Unique Dual Index Barcodes. They are also compatible with tagmentation-based workflows, such as Illumina® Nextera™ library prep kits.