Verel & The Lot
Are all man-made fibers, with Verel being a mondoacrylic polyester.
Unlike natual fibers such as linen and cotton, which previously had been ironed damp with a dry (and often hot and or heavy iron), man made fibers including rayon must be steam ironed.
For one thing being thermoplastic, man made textiles will melt at the temps used for cotton and certianly linen. Also any creases ironed in will be permanent.
These "wash and wear" or minimal iron fabrics required steam irons that not only produced steam at all settings (not all models did and some still won't), but kept the soleplate at the proper temperature to prevent scorching, melting and otherwise damaging fibers.
Steam ironing man made textiles actually prevents fiber damage and protects them from the heat from the iron.
P.S.
To get around the fact many irons then or even today will not produce steam or enough of it at low temperatures, ironing shoes were invented. These are the soleplate like things attached to a spring one sees for commercial irons, though they can be found then and now for home irons as well.
The idea came about as an evolution of the pressing cloth, and allows one to set the iron at it's highest temp without risking damage to whatever one was ironing. Thus one got to use the iron at it's full strength and get all the steam required.
Many older and even some irons today will not provide much steam unless set above "woolens" or even "cottons". An iron set too low will spit and dribble water because the soleplate/internal heat is not enough to create steam.
All irons, aside from those fed from steam boilers must create steam inside the unit, hence the problem. The physics of water cannot be altered inside the iron, that is water will "boil" or turn into steam only at a certain temperature. Thus makers have to devise clever ways to produce steam (even at low temps), whilst not making the soleplate so hot it will ruin man made fibers.