1,069,954. Treating fibrous materials. AEROJET-GENERAL CORPORATION. July 13, 1964 [July 12, 1963], No. 28880/64. Headings D1L and DIP. Dry packages of fibrous or filamentary material, e.g. beryllia, quartz, carbon, paper or glass strands, yarns or roving and cloth woven from suitable such fibres, are uniformly impregnated with a synthetic resin by a process comprising subjecting the package to vacuum, completely submerging the dry package in a liquid medium containing a heat curable synthetic resin composition which is substantially free of cross-linking, applying pressure to the liquid resin medium containing the package until the package has taken up a volume of resin medium substantially equal to Vm which is calculated according to the equation Vm=Vp-Wp/pr in which Vp is the exterior volume of the package being impregnated, Wp is the weight of the dry untreated package and pr is the density of the fibrous or filamentary material from which the package was prepared, removing the package from the unabsorbed liquid resin medium and heating it to convert the absorbed resin to a partially cured state and drive off any volatile material present in the package. The resin may be an epoxy resin, e.g. a polyglycidyl ether of 2,2 bis (4-hydroxyphenyl) propane, a phenolaldehyde resin, a urea formaldehyde resin, a melamine formaldehyde resin or a substantially linear ethylenically unsaturated polyester having a molecular weight of 500-10,000 and containing an ethylenically unsaturated monomer which is copolymerizable and miscible with the polyester, e.g. polydiethylene glycol maleate or polydiethylene glycol fumarate having incorporated therewith styrene, vinyl acetate, methyl methacrylate or vinyl chloride. The resin composition may contain a curing agent, e.g. hexahydrophthalic anhydride, methyl bicyclo (2.2.1) heptene-2,3-dicarboxylic anhydride, benzyl dimethylamine, dodecanyl succinic anhydride ethylene diamine, cobalt naphthenate or benzoyl peroxide, and a solvent, e.g. acetone, methyl ethyl ketone, methanol, butane or benzene. In Fig. 1 the impregnation is carried out in a vessel 1 having a vertical pin support 13 for the package 2 and supplied with resin media from storage tank 4 by line 5 the amount of resin added being continuously recorded on recorder 14 and controlled by valve 3. The liquid level device 10 operates a liquid level indicator 11 via conduit 12. Before introducing the resin into the vessel 1 the vessel is evacuated through line 7 having a valve 9 and fitted to a vacuum pump. The valve 3 is then opened to allow the resin media to flow into the vessel until the level rises to the top of the package, the level being observed on level indicator 11. To impregnate the valve 3 is opened until recorder 14 indicates that an additional amount of resin Vm has been added and impregnation is continued until indicator 11 shows that the level of resin media in the vessel 1 has returned to that corresponding to the top of the package. Line 6 leads to a source of inert gas under high pressure which may be used to facilitate impregnation. The package may then be transferred to the oven where it is mounted on shaft turned by a motor so that it continuously horizontally rotated during heating. The oven is heated by heating elements and the temperature is determined by a temperature detector which operates a temperature indicator. The oven also has a vacuum line and the pressure within the oven is measured by a detector and shown on an indicator. The heating may be carried out at a temperature from room temperature to 150‹F for 0.1-36 hours. The treated package may be stored in a refrigerated box maintained below 40‹F until ready to use, e.g. for reinforcing plastic structures.