The only detailed trapping experiments I am aware of were done with tsetse in Kenya (Brightwell et al., 1991). These authors compared catches in NG2G traps with cones made from different kinds of netting or thin cloth relative to a standard trap with highly-transparent white nylon netting. Catches were mostly related to the amount of light transmitted through the materials. Hence, catches were low with slightly opaque cloth, and high with light-coloured netting, or netting with a very wide mesh. I have obtained similar results with tabanids and stable flies in Canada during comparisons of a few retail products.

These values may differ from manufacturer's specifications. Spectral transmission data are available for many materials, along with colour indices at Research Resources.

Economical traps can likely be made with most insect screening or mosquito netting intended for outdoor use, so long as it is not too dark. I have been using fine white polyester mosquito netting as an economical standard for several years (Barre Army/Navy, Type IN-06).

Note that white netting often contains optical brighteners, and hence, is fluorescent. Ultraviolet protectants are also used, so transmission of ultraviolet light as opposed to visible light may vary among similar products. Additives, as well as fabric finishes, may also change without notice as retail suppliers respond to market supply and demand (most netting is made in Asia). Effects of the more subtle properties of materials on fly behaviour have not been studied. These fine details may be important, given the sensitivity of biting fly vision to both polarized light and to ultraviolet light.

84, 55% Fine mesh white polyester mosquito netting, about 529 holes per square inch, Type IN-06 from Barre Army/Navy in Vermont, USA (2003)
Recommended - economical netting that should last for about 2-3 seasons, tested in numerous experiments, easy mail order

81, 56%, Typical mesh white polyester mosquito netting, about 196 holes per square inch, Type IN-01/02 from Barre Army/Navy; this less expensive netting becomes fragile after just one season

82, 57%, White polyester mosquito netting, about 480 holes per square inch, from an entomological supplier in California, USA
Type 7250A from Bioquip

80, 67%, Grey "No-seeum" netting, about 625 holes per square inch, very fine weave retains biting midges such as Culicoides (similar material sold as IN-08/09 by Barre Army/Navy), numerous retail sources

61, 61%, Olive drab mosquito netting, about 196 holes per square inch, Type IN-05 from Barre Army/Navy, typical material in bug jackets, head nets and tents

60, 60%, Green polyester netting, about 480 holes per square inch
Type 7250B from Bioquip, very similar to olive drab netting above

65, 66%, Black aluminum window screening, about 288 holes per square inch,  New York Wire, highly transparent but shiny, cannot be sewn, but could be useful for applications where birds attack netting

58, 58%, Charcoal fibreglass insect screening (vinyl coating on fibreglass), about 225 holes per square inch, Bay Mills, typical material in windows, doors, porches, many similar products, e.g. in lighter grey
Readily-available, practical, strong screening that will last four or more years, BUT use of this material will reduce catches of some biting flies

I have also tested  a semi-opaque Nzi trap made entirely out of blue, back and white mesh. This all-mesh trap caught many tabanids, and hence may be useful in a windy or dusty environment. Unfortunately, it was a very poor trap for stable flies.

Generic Advice

Whatever you choose, it should be highly-transparent and uv-protected. The effect of using products that also block ultraviolet light is still under study.

Insecticide-impregnated mosquito netting may be useful, but I am unaware of any tests with biting fly traps. Information on the many options now available can be found at the World Health Organisation. Although impregnated netting has not been approved for sale in Canada, this material is for sale incorporated into impregnated bed nets for malaria prevention (HealthBridge). Bed nets are a worldwide growth industry with many ongoing developments at several manufacturers.

86, 68%, VF white polyester mosquito netting (2003), 12 x 13 mesh, 156 holes per square inch, typically impregnated with deltamethrin for use in bed nets for malaria prevention, see details of Permanet ® 2.0 in Mesh Sizes

89, 70%, VF white polyester mosquito netting (1997), 9 x 9 mesh, 81 holes per square inch, used extensively for all kinds of tsetse traps in the late 1990's by many researchers - Vestergaard Frandsen A/S

86, 64%, White polyester mosquito netting (1996), 15 x 20 mesh, 300 holes per square inch, used at CIRDES in Burkina Faso in West African tsetse traps in the late 1990s, purchased locally
Ouagadougo, sample from Sandrine Amsler-Delafosse

60, 61%, VF black polyester mosquito netting (1997), preferred over white by some tsetse researchers in the 1990's, e.g. for F3 or Epsilon traps
Vestergaard Frandsen A/S

65, 64%, Fine black synthetic netting, used as transparent inserts in the very first electrocuting nets developed in the 1970s in Zimbabwe, sample from John  Hargrove obtained in the 1990s

48, 46%, Black synthetic netting, used as inserts in electrocuting nets supplied by Bonar Industries in Zimbabwe in the 1990s to tsetse researchers, rather opaque netting, unknown source

63, 46%, Light brown 32-mesh Saran® screen (PVDC), used in Canopy traps for tabanids in USA, sample from Lane Foil (1996)
Chicopee Manufacturing, Gainesville, Georgia