Especially with 250gsm and 300 gsm, which are quite a stiff cards. CIE Whiteness (ISO 11475) - 145%. GSM is the weight of the paper, not the thickness. A3 297mm x 420mm (11.7" x 16.5"). A4 210mm x 297mm (8.3" x 11.7").
Great Printers for Printing on Card - Printerbase News Blog
3 x 5 Chipboard - Bulk and Wholesale - Fine Cardstock
A4 SHEETS OF CRAFT paper (white, ivory, cream, linen, smooth
A2 A3 A4 A5 A6 White Card Making Thick Thin Paper Cardboard
A5 148mm x 210mm (5.8 x 8.3). A2 420mm x 594mm (16.5 x 23.4). CIE Whiteness (ISO 11475) - 145%. A3 297mm x 420mm (11.7 x 16.5). A6 105mm x 148mm
WHITE THICK THIN CARD MAKING A6 A5 A4 A3 A2 PAPER SMOOTH REAM SHEET BOARD STOCK
A6 A5 A4 A3 A2 WHITE CRAFT DECOUPAGE CARD MAKING PAPER SHEETS PRINTER 120 300gsm £1.80 - PicClick UK
Gocreate A4 Thick Cardstock, 32 Sheets 250gsm Card Stock Paper for Card Making Scrapbook Holiday Party Decor Education Game, Metallic
A4 White Card 160GSM Box
A4, A3 Premium White Smooth Craft Paper Card Inkjet Laser 90gsm - 400gsm
A5 A4 A3 A2 A1 A0 White Cardboard Corrugated Sheets Pad Divider
120 Sheets A4 White Cardstock Thick Paper, 74lb White Card Stock Printer Paper, Heavy Weight Cover Card Stock (200 GSM) for Invitations, Wedding, Stationary Printing : Arts, Crafts & Sewing