SENTINEL®Welded Construction Filter Bags Now, applications requiring polypropylene or polyester felt filter bags can take advantage of the all welded construction afforded by patented SENTINEL Filter Bags. These bags are made from silicone-free materials and are produced with a proprietary construction process. This process results in fully welded, strong reliable joints with no chance for by-pass or loose threads. Seams are strong as well as flexible, allowing the bag to conform to the bag restrainer basket. The patented SENTINEL sealing ring guards against any possibility of by-pass. The seam edges of each filter bag are heat sealed, eliminating possible loose fibers. This results in a filter bag with durable performance for the most demanding applications. Available in 01 and 02 sizes with micron ratings of 1 to 200.