Bag Material for bag-type foot protection (Kyowa Filter Unit S type; standard type; reinforced type; mat type)

Fudo Tetra acts as a dealer for Kyowa Filter Units, a leading brand of bag material for foot protection widely used for rivers and waterways.

With Kyowa Co. Ltd., the manufacturer of this product, we have jointly developed the Filter Unit S type, a material for bagged foot protection work which we had in mind for use under wave action conditions. As sole agent we are working to promote and spread the use of bagged material for marine locations. We recommend Filter Unit S as bagged material for marine purposes, due to its outstanding wave-resistant stability and resistance to wear.


  • The use of a binding rope suppresses the movement of the material inside, boosting its stability under wave action.
  • To prevent rupture, 2 branches raschel net is used, which has 30% better resistance to wear than conventional products.
  • Stability parameters (N value) needed for weight calculation planning for cladding work are supplied.
  • Flexible formations fit well onto the surface beneath, and can be placed even where the surface is only roughly finished and uneven.
  • Bags can easily be stored and transported, shortening production time and lowering costs.
  • If concrete rubble Is used as the filling material it promotes recycling.
  • Voids in the filling material create a growing environment for all types of living creatures.

Product Specifications

For 4t (MS) For 6t (MS) For 8t (MS)
Form Bag (single layer)
Type Wave resistant, bound type (moss green color*)
Net Recycled polyester 2 branches raschel net
Net make-up 1670dtex x 33 x 2
(2 branches)
1670dtex × 45 × 2
(2 branches)
1670dtex × 57 × 2
(2 branches)
Mesh size 50mm 50mm 50mm
Net strength Tensile strength >2,600N per strand Tensile strength >3,400N per strand Tensile strength >4,000N per strand
Capacity Approx. 2.5m³ Approx. 3.7m³ Approx. 5.0m³
Filling material Pebbles, broken stone, concrete rubble (75mm to human head size)
Weight 3.8t to 4.2t** 5.7t to 6.3t** 7.6t to 8.4t**

* Moss green net used for S type has identical weather resistance to black nets, and fits better into natural surroundings.

** Weight varies according to specific gravity and size of filling material

Stability against wave action

Stability parameter N values when Filter Unit S type is used as cladding for embankments are as follows:

  • 【Marine】wave-dissipating work, foot protection, sloping embankments, offshore breakwaters, artificial reefs, jetties
  • 【Waterways】Foot protection, groundsill work, spur dikes, coffering


Assembly is done through an easy procedure as with conventional filter units.

Set the bag in the frame

Fill with filling material by machinery

Tie up the mouth of the bag (pull out the binding rope)

Remove the frame

Withdraw the binding rope and tie



Weather resistance of the Filter Unit’s net has been certified as sufficient through indoor testing to JIS standards.

  1. Wear resistance: the product has not yet been long used on site. We therefore recommend its use inside bays, for foot protection, cladding, sand barriers, preventing scouring, or as a base for seaweed beds.
  2. For use in the open sea, where there is considerable movement of sand and gravel on the seabed, we recommend careful study prior to use.

Cases where used:

Armor unit for rubble mound within harbor

Foot protection for disaster rehabilitation in coastal area

Foot protection for gentle slope revetment

Armor unit for breakwater mound (hydraulic model testing photo)