Following his ninth straight day of training at the 49ers training facility, next to home ground Levi's Stadium, Hayne said the equipment used in the NFL makes it a totally different game to what he played in the NRL.
"The biggest thing is that you wear a helmet and pads," Hayne said.
"I played third man in (centres) in league as well where I made a couple of tackles.
"I didn't really like that it kind of reminded me of practice today getting your head in and making sure you're running through the right gaps."
"There's a huge amount of contact and with the helmet and shoulder pads you go a lot harder into contact with a lot more force."
With NFL teams only allowed to have 14 padded practices in pre-season – a means to limit player burnout and injury - Hayne only just started using proper hard pads this week.
However he said the transition from using soft pads (shells) to the bigger, harder pads was easy.
"I actually felt better (wearing pads)," Hayne said.
"We've been wearing shells for the last week and I actually thought the shells were a bit heavier.
"When you sweat the shells get heavier and heavier and the pads are a bit lighter, obviously stronger, but I felt good in them and ran fine in them as well."
The 27-year-old also described where his focus is in his attempt to develop into an NFL quality running back, one of the toughest positions to play in world sport.
"As a running back you've just got to really know where you're running and who you're running off and anticipating what the defence is going to do, all the great running backs do that," he said.
"It's just getting those techniques and obviously trying to find the gaps for holes in the defence."
"I've just gotta keep learning and keep getting better, the biggest thing is just technique.
"It doesn't matter what sport you play or what profession you're in it's all about technique and experience."
The former Eels and NSW Blues star also revealed that the easiest transition between sports is returning kicks and punts, a skill he has great experience with in his time playing at fullback.
"I wouldn't say it's (catching is) easy but it's definitely something that I could adapt to fairly quick.
"It's still tough to catch those balls, the NFL ball rotates a lot faster than a rugby ball and so it moves a lot quicker but when it moves a lot quicker you can define where it's going to land.
"Those rugby style kicks are when the ball rotates and when it comes down it's flat it's on it's belly.
"When it's like that it's pretty much game over for a returner because it can deviate from five yards to ten yards so it's tough."
Finally Hayne said the toughest part of the contact training was running straight into 111-kilogram linebacker Nick Moody while fully padded up and without any blockers between them.
"It was pretty tough drill we don't really get a clean run like that at a linebacker they're normally going around a (blocking) guard or a centre or trying to disguise their blitz.. I'm glad I got through it."
"Going head on with Mooney my neck's pretty sore, I've gotta keep working on technique."
Hayne said that he was looking forward to getting home and enjoying a day off by playing some FIFA and sleeping having spent long hours at practice for nine straight days.
First day in pads. Learning n tryn to get better every day. #trainingcamp #49ers https://t.co/fsnsyuSKpB
— jarryd hayne (@jarrydhayne_1) August 5, 2015