pwcphoto wrote:
You can go to Home Depot and get the white plastic flourescent lighting grids. They come in 2x4 feet sheets in a grid pattern made of 1/2 inch squares. Cut the sheets to size or glue multiple sheets together if you need something larger. Paint the sheets with matte black paint and glue Velcro strips along the edge to attach it to the softbox. If you need more directivity you can place one sheet over the other to increase the thickness which is about 1/2 inch or so. They are a bit heavier then a cloth grid, so you may need to put a light stand under it to give added support if your softbox cannot handle it. The sheets run about $5 each plus the cost of the paint, glue and velcro. They work quite well.
Sort of an add-on to that, but potentially lighter would be air vent filters. There are a variety where the grids are hexagonal and are quite light, made from compressed paper fibers. Same idea as the flourescent grids(velcro/glue to gether to make bigger, cut to make smaller).
Awesome link to the homemade softgrid and to the technical explanation page of the degrees.