This is a complex subject and there is many different ways to protect palms.
Firstly please read in conjunction with the article on Palm Hardiness which explains the limits of the various options available and when to take action.
I would also suggest people join the various facebook groups such as the European Palm Society or Hardy Tropicals or UK Tropical Look Gardening to give a few examples. Yorkshire Kris offers wonderful Youtube videos.
There you can see many examples of ways people protect palms .
Personally, I am something of a minimalist, most of our hardy palms are fully equipped to deal with the vast majority of winter without any protection at all. Very often you can kill your palm with kindness, without air circulation and trapped moisture, fungus soon takes hold. Plastic is particularly nasty and will leave unsightly brown marks on leaves where it is in contact.
The best option is to do nothing and to stay tuned in to the local weather forecasts and be prepared to act quickly for a severe weather event.
Its important to know your palms limits ( detailed in the separate blog , how hardy is my palm ) and to ensure the protection you use adequately keeps them within those limits.Trachycarpus for example is unlikely to need any protection, whereas a Butia or Phoenix will. Horticultural fleece is an excellent tool , but only helps with 2 or 3 degrees of frost protection for short periods of time.
If a severe weather forecast is made then more robust protection is likely required. Bubble wrap can be used to insulate trunks for short periods of time. Alternatively any insulating material can be used , carpet, duvets, blankets, tarpaulins , it doesnt really matter. Stuff fleece into the area around the emerging spear. Tie up the leaves and insulate sufficiently to prevent cold penetrating into the heart of the palm.
Christmas lights ( non LED) wrapped around the trunk inside the insulation, but not in direct contact with the plant will help to prevent the trunk freezing. Insulation of the ground with mulches is a good idea also.
Some people will construct a plastic roof to keep the plant dry and to prevent radiational freezes. This will also reflect heat leaving the ground back onto the plant, but obviously this only works for small plants.
Ultimately , the action needs to be in line with the severity and duration of the forecast, and the time to take action are those long day and night freezes in December, January and February when the temperature doesnt rise above freezing. When the daytime temperature rises several degrees above freezing its rare for the palm to require any protection.
There is no limit to human ingenuity and there is many more ways and materials to protect a palm tree, but hopefully this gives enough pointers to guide you in the right direction. Usually its about doing enough to prevent the cold penetrating right into the heart of the palm itself and thats something that only the individual can judge based on his own location and the forecast itself.