IK heb een antwoord gekregen van Helisport:
"Geachte heer XXXXXX,
De BumperPlates van PowerMark zijn absoluut echte BumperPlates, bij deze voeg ik u ook nog de mail en PDF van onze fabrikant toe.
Of course they are bumper plates, but it has a inner steel core, sketch
enclosed for your review. This is the most popular and common construction
for bumper plates in the market currently, IWF sponsored manufacturers,
Eleiko are all doing bumper at this construction. We did 100% rubber bumper
plates several years ago, but all changed to this construction now. 100%
rubber bumper plates are also very thick, you can load very few plates onto
a bar.
As to the hardness of bumper plate, actually IWF has standard, the bumper
cannot be very soft, it should not bounce high and many times as it may hurt
lifter. And in production, it is easier to make it soft but not easy to make
it very hard.
These bumpers are sent to several countries for several year of testing,
especially sent to US for heavy using, so you can be trusted in the quality.
Mocht u nog vragen hebben betreffende mail hoor ik dat uiteraard graag.
Met vriendelijke groet,
Robert Verschraagen
Verkoopadviseur
Helisports International
H.J.E. Wenckebachweg 83
1096 AL Amsterdam
Tel: 020 - 693 99 39
Fax: 020 - 663 90 69
Internet:
www.helisports.nl
E-mail:
r.verschraagen@helisports.nl"
Ik moet zeggen dat ik dit toch wel overtuigende info vind. Hier de sketch van de plate die ze er in bijlage toevoegden:
