I am the new coming for this area. Trying to buy some carbon fiber materials but being confused about so many options.. what is the different between these two and how to choose it based on the application?

You need both. The Easy-preg surface layer is specially formulated to be used as the first layer into the mould to provide the best cosmetic results when used out-of-autoclave, whilst the vari-preg is used as the backing layers. 

Thank you so much! 

Nope, these are perfect as long as you have an oven and the tooling to handle the cure cycles. 

If you are looking to do "out of autoclave" pre-preg then you will need the Easy-Preg Surface Layer PrePreg Carbon for the surface layer to help get a good cosmetic layer. The backing layers are made up of the Vari-preg pre-pregs but typically for most none structural parts a common layup is one layer of Easy-Preg backed up with one layer of Vari-Preg430g 1.27m Wide giving a total thickness of 0.75mm.

I recommend you read our Beginners' Guide to Out-of-Autoclave Prepreg CarbonFibre and watch our tutorial videos as it explains all the basics in detail and should make it clear how the layers work.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I dont want to be rude and I always encourage people trying stuff, but prepreg is not the easiest thing to start with... 

I have watched this video https://www.easycomposites.co.uk/learning/how-to-make-complex-multi-part-split-moulds 

It wasn't an autoclave oven that was being used, but a conventional electric oven with vacuum fittings incorporated

If my rough conversion of the 42.5 l/m is right, then I think that would be around 1.8 c/f per minute displacement, though I'm sure someone will be along soon to correct that if I'm way off.

As already stated, the smaller of the two EC pumps is more than capable of handling all but very large pieces in a reasonable timeframe. It would still work on even large vacuum bags, but would take a lot longer to evacuate the air than a pump with a bigger capacity.

What you see in the video is an oven NOT an Autoclave. Our Easy-Preg pre-pregs are designed to get a good surface finish in out of autoclave curing processes.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

The principal difference between "out of Autoclave" and "autoclave CF work is that the Pre-preg CF used for Autoclave work, relies on the autoclave being able to produce a pressure on the CF layers in the mould that is higher than +1 Bar/Ato.   Heating cycles and Ramping up of temperatures is needed in both cases .. using more then two layers of prepreg most often requires "bebulking" of the first layers, before adding more layers. often Autoclave Prepreg uses (or can use) a higher curing temperature ... The ramping up is required in order to first get the resin in the prepreg to flow and the CF layers to compress. If you go to full cure temperature too fast the resin will not have time to flow and the CF layes may not consolidate properly.

IMHO successfull "Out of Autoclave" prepreg work requires a properly controllable oven, with vacuum feed-through connectors.

Starting CF work using "out of Autoclave" Prepreg is perfectly possible, You will just have to accept wasting quite a bit of expensive Prepreg in geting to know the niggles with vacuum bagging, layup and mould work, without the the benefit of experience with the "wet" methods ..

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