From the manmufacturer:
Whether you are an experienced artist or a creative crafter, the distinctive texture and quality of Strathmore Creative Cards are the perfect way to personalize your correspondence. Ideal for colored pencils, rubber stamps, die cuts, collage and more.
Announcement Size Creative Cards This small card is ideally suited for formal announcements, gift enclosures, invitations, change of address and thank you notes. Announcement Size envelopes are 3.625" x 5.125". Announcement cards meet domestic size requirements for US 1st Class Mail.
Full Size Creative Cards These larger size cards can be used to design a greeting for any occasion from birthdays, holidays and invitations to general correspondence. Full Size envelopes are 5.25" x 7.25".