The better helmets offer spare pads, buckles or straps aftermarket. They do vary in design depending on what you need them for.
Below is a short description of different types used by the average ebike rider & where to get them at a decent price.
For improved protection, mountain bike ( mtb ) helmets have extended coverage at the back of the head in case of tumbles off road involving rocks, trees etc. Fewer but larger vents help the heat escape when grinding slowly up hills. They come with a removable visor to prevent branches poking the wearers eyes out. Some have a bug net fitted to stop midges. A hardshell outer leaves less exposed polystyrene, so protecting from off road hazards. Prices start from £10 at On-One online, £12 for Abus S-Cension from Go Outdoors.
For those wanting something a little lighter and less bulky there is the road bike helmet. Typically have more vents than other types, designed to increase air flow when travelling at speed. Less coverage at the rear but more aerodynamic. Removable, anti- bacterial pads fitted for hygiene. Carnac helmets from £8 at Planet-X online or B'twin helmets for £15 at Decathlon.
Commuting helmets; most have large vents to let heat escape while at low speed. Reflective decals are widely used for increased visibility in low light conditions, and rear lights built into the cradle. Neon colours are widely used by manufacturers. Prices start at £10 for a 100 City helmet from Decathlon.
From experience, commuting helmets are great in the winter, but for the rest of the year an mtb helmet is better in preventing heat build up when commuting and for general use.
All cycle helmets sold in the UK pass the same standards for safety. More expensive lids have a MIPS ( Multi-directional Impact Protection System ) lining which increases injury prevention in snagging impacts. Better helmets use an in moulded shell rather than a taped on outer. This provides more strength to the liner.
Manufacturers recommend replacing every 5 years due to the limited lifespan, plus they do get knocked around over that time. With new ones being ten a penny isn't it time for something new.