All of the posters above has some good point to add. But I just want to add that if you were to use white piece of paper, just be careful because some white paper have extra blue additive or some are slightly yellow (not visible under indoor light). These may throw the color off in your photography. You can experiment and for the most part you will not have any problem (but just keep the above in mind if you get a color cast).
Also, the size of the reflector makes a difference. A single 8x10 paper will do for flower the size of a rose. But if you were to take a picture of a dozen roses then it would not be enough. Also an 8x10 on a single rose can actually create reflected light directionality (and create obvious shadow on the opposite side). But use a larger reflector and the shadow will be much softer or even gone.
And like so, for a face shot, you would need a minimum of 12 - 24 inch reflector (across). For a full length of a person, you would need something about 6 feet in height.
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Usually the silver reflector (crumpled aluminum foil) on overcast days. On sunny days, the silver reflector side will be too harsh.
Here's a little known fact about reflector: you can create BLACK reflector. People call it black REFLECTOR but in actuality it is a light absorber. Sometimes you could be in a situation where the lighting is just too flat (even lighting everywhere). By using a BLACK REFLECTOR, you "create" a shadow area on one side or another
Reflectors are not expensive. So once you are done experimenting try one of these:
http://www.bhphotovideo.com/c/product/358606-REG/Impact_R1122_5_in_1_Reflector_Disc_.html
http://www.bhphotovideo.com/c/product/358607-REG/Impact_R1132_5_in_1_Reflector_Disc_.html
Good Luck
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