These are legally protected and are to be used only when you are writing about the genuine article. Many firms scour the media for incorrect references to their products and then complain or even sue. This is because they may lose the right to the trademark if they fail to protect it. If you are not certain, use a generic alternative. Some are suggested below. Trademarks (note: one word) always take a cap. There are many more than these, so do be wary.
Adrenalin: the synthetic form of the hormone adrenaline
Aertex (not Airtex): cellular cotton fabric
AstroTurf: artificial grass
Babygro: babygrow, all-in-one
Biro: ballpoint pen
Botox: cosmetic treatment
Catseye: cat’s eye or reflecting stud
Cellophane: transparent wrapping
Coca-Cola, Coke: fizzy drink, cola, soda
Corn Flakes: the original branded product made by Kellogg’s (note apostrophe). The generic term is cornflakes.
Elastoplast: sticking plaster
Filofax: personal organiser
Formica: plastic laminate
Frisbee: flying disc
Google: search engine, but can be used as a verb ‘to google’.
Gore-Tex: waterproof/breathable fabric
Hoover: vacuum cleaner; but you can use it as a verb without a cap, as in ‘the dog hoovered up its dinner’. Some authorities say the word is now the generic word for vacuum cleaner and has lost its right to a cap.
Identikit: but photofit is not a trademark.
Ironman: only triathlons organised by the World Triathlon Corporation (WTC) may be called Ironman events. Others over the same distances may be referred to as a full- or half-distance triathlon, or an Iron-distance triathlon.
Jacuzzi: whirlpool bath
Jeep: four-wheel drive vehicle; note that jeep is acceptable for the small vehicles used in the Second World War, the name deriving from the initials GP for general purpose vehicle.
Jiffy bag: padded envelope
Kleenex: paper handkerchief, tissue
Li-lo: air mattress, air bed
Lurex: sparkly fabric
Lycra: stretch fabric
Martini: a brand of vermouth as well as other alcoholic drinks - as a trademark it takes a cap; a martini (l/c) is the cocktail containing vermouth.
Monopoly: board game
Muzak: imagine anyone wanting to claim ownership of that.
Ouija board: there isn’t an alternative.
Outward Bound: survival course.
Pepsi-Cola: fizzy drink, cola, soda
Perspex: acrylic sheet
Photoshop: digital image editing or airbrushing; it is ok as a l/c verb eg ‘He photoshopped the picture to erase Hitler’s moustache’.
Plasticine: modelling material
Play-Doh: play dough
Portakabin: portable building; Portaloo: portable toilet.
Post-it (l/c ‘it’): sticky note
Pot Noodle: instant noodle snack
Pritt Stick: glue stick
Puffa jacket: padded jacket
Q-tips: cotton buds
Quorn: vegetarian meat substitute
Rawlplug: wall plug
Rizla: cigarette paper
Rollerblade: in-line skates
Scrabble: board game
Sellotape: sticky tape
Semtex: plastic explosive
Spam (the meat product): chopped pork and ham, canned processed meat
Stanley knife: utility knife
Stetson: cowboy hat, western hat
Tannoy: loudspeaker or public address system; ok to use as a l/c verb eg ‘he tannoyed a warning’.
Tarmac is a trade name but can be limited to the name of the civil engineering firm. The l/c tarmac is acceptable for road surface. Note: Although tarmac is often used as a shorthand for the surface at airports (eg ‘The Pope kissed the tarmac’), apparently very few airports have tarmac runways any more. They are now concrete.
Taser: This one is still bedding in, but I think it can be treated like Hoover, used with a cap as a noun but lower case as a verb. For example: ‘They should not have tasered him’.
Thermos: vacuum flask
Tipp-Ex: correction fluid
Vaseline: petroleum jelly
Viagra: still working on this one
Walkman: personal stereo
Winnebago: large motor home, recreational vehicle
Yale lock: pin tumbler lock
Yellow Pages: trade or phone directory
Zimmer frame: walking frame