25cm x 100cm Gravel bags come in pack of 20. When filled with 2cm pea gravel they weigh approx 15Kg. ensile gravel bags are made from tough, long lasting, flexible materials to hold your silage covers firmly in place. Due to the flexibility the bags are able to follow the contour of the silage, and make a much better seal against the silage clamp wall than tyres. Each bag has a carry handle and built in drawstring tie.