The Welwyn Garden City site was known as Barnet Combs where many items, including combs, were produced. The building was very close to the Shredded Wheat factory, Knorr Soups, Polycell (which occupied an old film studios) and a cigarette factory. Almost next door was Devices Ltd who manufactured the first heart pacemakers.
The R & D department was where they developed PVC bottle blowing techniques.
This all closed in about 1968 and all production was moved to Lavenham*.
(*Many thanks to an ex-worker who provided me with this information).
From another ex-worker, Brian Cook:
“When Barnet Combs was taken over by Holpak (a subsidiary of Unilever), they had a production factory built on the out skirts of Glemsford, not far from Lavenham. One of the main products was the Ski yoghurt pots, Fairy liquid bottles, Parazone bottles, Domestos bottles and injection moulded products. There was a small repair tool room, but if a major breakdown occurred then a toolmaker / toolmakers would be sent from here in Welwyn Garden City, often overnight stays,weekends too (production came first). The factory site was by the banks of the river Stour, on the Clare - Long Melford road, (the factory is no longer there).”
To read more quotes from Brain and to see some of his photos, please click this link:
From here: http://www.gracesguide.co.uk/E._R._Holloway
E. R. Holloway of Hyde Way, Welwyn Garden City, Herts. Telephone: Welwyn Garden 597. Cables: “Allkombs, Welwyn Garden City”
1947 British Industries Fair Advert for “Barnet” combs and slides – for reliability and durability. Manufacturers of the “Barnet” Series of Hair Combs, Hair Slides and Sundry Articles. Proprietors of Lustrac Plastics Limited, Manufacturers of “Lustrac” Cellulose Acetate and Vinyl Acetate Injection Moulding Powders. (Plastics Section – Earls Court, 1st Floor, Stand No. 790) 
1950 A substantial interest was acquired by Thomas Tilling.
The Holloway Group of Companies
In step with the growth of plastics, the Holloway Group continue to expand their range of products, made both here in Welwyn Garden City and at Glemsford in Suffolk.
Although Britain’s largest hair comb manufacturers, the Group have extended their activities to more and more other fields, from brushware to sunglasses, including plastic components and containers that serve other industries; and the subsidiary, “Lustrac Plastics,” makes raw material for both the Group and outside customers.
Local people, however, will be most familiar with “Barnet Comb Company” which is the Group’s manufacturing company with its main factory in Hyde Way, Welwyn Garden City.
E. R. Holloway’s Ltd. warehouses and offices operate in Bessemer Road. From here the Group products go all over Britain and the world; and despite the increasing size of the company the character of a family business is still preserved, under direction of Holloway brothers in active management.
The Group employ highly skilled tool makers and engineers, machine operators, finishers, assemblers and packers, beside other warehouse and administrative personnel.
Plastics by E. R.Holloway Ltd.
The association of the E. R. Holloway Ltd. group of companies with Welwyn Garden City dates from 1934 when they transferred from Southgate a small factory engaged in the finishing of vulcanite combs.
The story of the progress of E. R. Holloway Ltd. and their associated companies may not be remarkable, but it is typical of that of the many family businesses whose contribution to the prosperity of this country has been so invaluable. A limited company was formed in 1924 and offices were taken in the City of London, but not until 1931 was any manufacturing done, and then it was only the finishing, by processes that now seem crude and laborious, of vulcanite combs. From the time when this small factory of the Barnet Comb Company arrived in the Garden City the manufacturing side of the business began to go ahead until within a few years almost all the goods sold by E. R. Holloway Ltd. were the products of their own subsidiary.
In 1938 the warehouse and offices left the City for the more attractive and convenient site adjacent to the factory. Since then and indeed even before, the record has been one of constant experiment and innovation, and of almost equally constant growth. An injection moulding machine was installed in 1936 and the Barnet Comb Company produced commercially the first injection-moulded comb in this country.
Lustrac Plastics Ltd., a further subsidiary, was formed in 1943 for the manufacture of moulding powders. This in turn proved a success. Not only were its cellulose acetate powders wanted for the group’s own products, but a prosperous trade was built up with outside moulding firms. This company has now turned its attention to other materials besides celullose acetate and has extended its activities to include extrusion processes. It is thus able to meet the growing industrial demand for such articles as shaped rods and tubes.
The most recent addition to the group is Hydeway Ltd., a company started in 1949 for the production of welded plastic goods such as wallets, bags and purses. Again healthy progress can be reported.
For over thirty years now, the aim of the directors of this group has been to give a quality and a service second to none. The results speak for themselves. Since the end of the war, in spite of raw materials shortages and of increasing competition, the output of the group has increased by over 300 per cent in volume, and the increase by value has been even greater. Moreover, since a high proportion of its goods are sent overseas, the group has the satisfaction of knowing that it is making its contribution to the nation’s export drive.
Throughout its history good relationships have been maintained between management and employees and every attention is given to the improvement of working conditions. For several years now all employees after three months’ service participate in a profit-sharing scheme.
Barnet Combs c1938.