sentences:  While in 1976 there were roughly 100 cellulose insulation firms with 125 plants, by 1978 there were more than 350 firms with more than 500 plants1.Cellulose insulation was produced locally by small manufacturers who purchased ready-to-operate machines and offered a cheap and easy low-tech production process.Other than some constraints created by a shortage of boric acid for use as fire retardant, cellulose captured an increased share of the market due to lower costs and its suitability for retrofits.