Those canings appear to have been given with a fairly typical school-type cane (not a thick heavy one like the Singapore rotan) but, judging by the article, both girls had pretty severe marks afterwards. The girl describing the caning says that she had to take off her dress and pantyhose but says nothing about taking off her underwear, so the canings were presumably administered over panties. Nevertheless she said that she had never felt anything so painful! Just shows that you really don’t need a thick heavy cane to produce plenty of pain.
Also, it’s interesting that the Malaysian authorities considered that the girls had been treated leniently as a teenaged boy had previously been given 12 strokes for a similar offence. No doubt that would have had Jenny up in arms (and quite rightly!).