Storing cards in top loaders has been a common way of keeping cards protected and in good condition for a long time now. These flat, little pieces of plastic have been around since I can remember! As a kid, there was only once size of top loader. Now, there are a bunch... so you might be thinking which ones to use when? Let me help you out today.
My top loader of choice is made by Ultra Pro. Ultra Pro has been making plastic holders for cards, photos, and other items for quite a while. You'll find Ultra Pro products at most hobby stores. For those new to card collecting, top loaders are best when used in conjunction with a penny sleeve. Put the card you want to protect in a penny sleeve first, then put the sleeved card in the top loader. This will provide great protection for your card. If you're like me and want to be extra protective, you can put the entire top loader/sleeve/card combination in a team bag.
The 3"x 4" regular top loader is the standard top loader for base card thickness cards. These are great for Young Guns and thin autographs. Often times you'll find a pack of 25 of these with a free small 25 ct. pack of penny sleeves.
Slightly larger are the 3" x 4" SUPER thick top loaders. These hold cards up to 75 pt. thickness and come in a pack with a grey cardboard holder. Most Ultra Pro cardboard holders are black... not sure why this one is different actually. This is probably the least used type for me. They hold cards slightly bigger than base card size. Older jersey cards fit well in these.
The 100 pt. thick top loaders are probably the most common ones that I get. These top loaders are the ones that fit the standard jersey cards very well.
130 pt. super thick top loaders are the kind you get for patch cards and cards from The Cup. 180 pt. top loaders are probably the ones at the end of the standard spectrum of top loaders, and these work well for cards that are very, very thick.
Hopefully this short guide will help you when trying to figure out what top loader size to buy. Let me know if you have any questions!